Age-gap relationships revisited and the denial of human biology
My basic position on adult-minor sexual/erotic contact or romantic intimacy is simple.
-Children and legal minors are harmed only by felt emotional distress. Risk-aversion can at least theoretically justify discouraging *AMSC but discouraging AMSC on the possibility that it might cause emotional distress doesn't capture the conventional attitude that AMSC is inherently bad, we can imagine a logically possible scenario in which AMSC did not immediately or ultimately cause the younger party emotional distress (I think this is an important point because people often use the value of trauma or felt emotional distress to legitimize negative value judgments about things that cause emotional distress circumstantially when we could theoretically have one without the other, so from an anti-suffering point of view we would have no reason to oppose x in scenarios when it did not cause suffering, nor would we have a reason to view harmless actions that don't imply de-valuing or positively valuing suffering as immoral; and I do believe that an action can be immoral or imply immorality despite being victimless and thus not an injustice. I think of injustice as harm + malintent or negligence).
-AMSC should be valued to the extent that it could be a source of happiness for minor-attracted adults (i.e. adults who aren't asexual) and legal minors alike, even if possible sexual happiness should be weighed against practical risks and costs of AMSC (so you can agree with these points so far and still oppose AMSC in practice, without viewing it as inherently bad or; by extension, the desire for it as inherently immoral). While there might be some possible universe where discouraging AMSC is practically justified, I believe that the stigmatization of true pedophilia (an attraction to, if not preference for, prepubescent children) and minor-attraction when felt by adults, as well as the idea that AMSC is inherently bad, is inherently immoral because it necessarily implies de-valuing happiness (viewing a thing as inherently bad primes you to have a negative emotional response to it, viewing a thing as inherently good also primes you to have a negative emotional response to its absence, so if you're trying to persuade people that AMSC or anything else is inherently bad you're effectively trying to persuade them that it shouldn't be a source of happiness. A state of affairs is bad if we are justified in wanting it to not exist, so the extent to which you view something as bad is the extent to which you would prefer that it not exist even when it could be a source of happiness for people. This is why I believe that the idea that anything other than suffering is inherently bad is immoral. By contrast, I see the idea that something other than happiness is inherently good; at least if it's something that doesn't have an opposite, as a philosophical error but not a moral failing, even though I believe the idea that only happiness is intrinsically good is the position that best helps us to make sense of reality and maximizing happiness at least circumstantially conflicts with serving other values).
-There are practical scenarios when AMSC could be a source of pleasure for prepubescent children, and even more certainly for pubescent/post-pubescent minors, without any unnecessary or long-term emotional distress or trauma. At the very least, in the absence of any anecdotal observations or personal experience, someone who agrees with me that experience is our only source of knowledge would have to concede the theoretical possibility since we can imagine such a scenario (we can't imagine a 4-sided triangle because having three sides is what makes a triangle a triangle), so AMSC doesn't have to cause the younger party pain (and unlike experienced desire frustration broadly, it doesn't necessarily prime a negative emotional response. It could be a source of happiness for minors). It isn't just that there are hypothetical scenarios where AMSC could be justified for a greater good but that there are scenarios where it wouldn't be bad at all or to begin with.
I could elaborate but a more detailed argument can be reduced to these three principles-only felt emotional distress is inherently bad, everyone deserves happiness and AMSC could possibly be a source of happiness for minors/not cause them unnecessary emotional distress or long-term trauma.
I believe there are serious logical problems in the conventional arguments against AMSC that have nothing to do with my philosophical hedonism per se that I should probably focus less on but I think are worth noting. One is the conflation between the absence of consent and something being against one's will (if it were true that children couldn't meaningfully consent to sex then they couldn't be deprived of a choice that they couldn't make to begin with, and if they couldn't make an informed decision to engage in AMSC they also could not make an informed decision to avoid it. Adults would have to make the choice on their behalf and a more coherent critique would be that an adult who engages in sexual intimacy with a minor has made the wrong choice on their behalf, rather than that they made it on their behalf. The very concept of parenthood is rooted in making choices on behalf of children). I think the idea that children can't consent to sexual intimacy is rooted in the meaning that people project on to it and as I mentioned long ago, a lack of wise or prudent decision-making doesn't negate a capacity for literal consent. People are also capable of consenting to experiences or contracts with self-aware ignorance (e.g. you don't know whether or not you'll like a novel you buy or a new food you've never tried or if you might be allergic to the latter) and the idea that minors can't comprehend the emotional consequences of sex would only apply if they were truly asexual which relates to a later point I'll make.
I also reject the arguments that center around power dynamics because a) all relationships involve power imbalances, because people are different and that implies variation in strengths and weaknesses and b) power imbalances are inherently neutral, the problem lies in the use of power to harm the weaker party but relationships with cognitively developed enough human beings probably always imply vulnerability and require trust for that reason. Under the anti-power disparity logic body builders shouldn't date scrawny women, high-IQ women shouldn't be interested in lower-IQ men, emotionally tough people shouldn't be in relationships with more sensitive people, etc. The concept of 'exploitation' is also meaningless without actual harm, if exploitation can be harmless the question becomes 'why is exploitation bad?' Depending on the age of the younger party, people with an anti-age-gap relationship prejudice seem to jump back and forth between the consent argument (the presumed inability to consent being rooted in cognitive underdevelopment or even asexuality) and the one about power imbalance, and there seems to be this misconception that even legal adults can't consent to a relationship that involves a power imbalance because they shouldn't. There is also no default increase in power that comes with age in a vacuum, a 20-something-year-old police officer is, in some respects, more powerful than a random middle-aged civilian, nor does anyone question the rational agency of an 18-year-old who murders an elderly person; they would be tried as an adult but treated as an honorary child if they were to voluntarily enter into a romantic relationship with that same elderly person (it's also not lost on me that physical prowess and cognitive ability decline with age, yet older people as older people are considered inherently more 'powerful'). There is a power imbalance between parents and their dependent children and between teachers and their students (although a relationship can involve different power imbalances that favor each party), there is no necessary power imbalance between every random adult and every random minor (the minor might view the older party as an authority figure by virtue of their age but they might be susceptible to peer pressure from similarly aged people as well. The older person might find the younger person more intimidating, this kind of personality variation exists in different age groups).
Fertility and attraction
The stigma around older adults (particularly men) being attracted to, pursuing or developing relationships with younger adults (particularly women) is often justified largely by a misunderstanding, if not dishonesty, about the nature of sexuality. If a normally sympathetic person loses their temper with an extremely disagreeable, cruel antagonist and resorts to some mild violence in the heat of the moment we understand that this is a normal human response, we don't diagnose him with 'Anti-Social Personality Disorder,' anger is an emotion that presumably all people are capable of so this kind of behavior is to be expected even if the provoked party is being irrational, unwise and unethical. Instead of making a straightforward moral argument for older men not acting on perfectly natural instincts the belief, or pretense, seems to be that normal and/or moral men naturally outgrow their attraction to young women once they reach a certain age, supposedly not having anything in common with them that could make them appealing romantic partners (they might be able to 'see that they're attractive' but they no longer have an instinctive desire for sexual intimacy with them, or for emotional intimacy in the context of sexual attraction), in fact; an older male interest in young women is often interpreted as a calculated attempt to exercise power over a less assertive or independent-minded partner rather than having anything to do with primal involuntary attraction.
I say that this involves a denial of biology because men are biologically adapted to fertilize egg cells. This doesn't just correlate with being male, it's what makes males male. The biological function of maleness is to fertilize egg cells, this is why male bodies produce sperm. Egg fertilization necessarily requires ovulation which neither prepubescent children or postmenopausal women are capable of, so we should expect that average men are going to prefer girls and women of normal reproductive age.
Although it's not not super rare for girls to have their first period as early as 8 or as late as 17, when malnutrition isn't an issue (because a girl's body won't prepare for pregnancy if it doesn't have enough fat to sustain it) the average age of menarche seems to more or less consistently remain at 12. Menarche is generally considered premature if it occurs before 10, at 13.75 around 90% of girls have had their first period, and it's considered delayed if it hasn't occurred by the age of 15; when around 98% of girls in a developed country have had it. Both perimenopause and menopause fall under 'primary ovarian insufficiency' when it appears before the age of 40. Menopause (being the permanent end of a woman's menstrual cycles, when the ovaries run out of viable eggs estradiol production comes to a virtual halt which explains the symptoms associated with menopause and why, in terms of health, men more or less tend to have a comparative advantage in middle-age/late adulthood) is considered early at 40; when around 1% of women have undergone it, and normal after 45; when around 5% of women no longer have menstrual cycles. At 55, around 90% of women have hit menopause and at 60 it's around 99% (any number between 48% and 1% seems arbitrary to me but researchers often consider a trait to be abnormal if it occurs in 5% or less of the population).
From a medical standpoint, the best time for a 'girl' or woman to get pregnant is from the start of Tanner stage 5 up until 25 (I'm assuming that Tanner stage 5 in girls is typically reached a year or two after menarche so if we assume that someone is a late bloomer but not to the point of it being medically abnormal, I think we can say around 17-24). Female fertility seems to begin gradually declining as early as 25 and the risk of various pregnancy complications rises at that age. Apparently, from 16-25 a woman who's trying to get pregnant has an around 86% chance of successfully conceiving in one year, from 26-29 it's around 78%, from 30-34 it's around 63%, from 35-39 it's around 52%, at 40 it's around 44% and at 45 it's around 5% (stats might be different from source to source). After 45, around 53% of pregnancies end in miscarriage.
Considering that men's bodies are adapted to impregnate women and most men produce sperm until the day that they die, it shouldn't be surprising if average men prefer girls or women who look as though they are around 13-39, or even 13-44 (the super-ideal might be 17-24). I feel bad in saying this because I genuinely don't want to be cruel, I have always maintained that I don't think anyone's appearance is inherently beautiful or flawed, but I think this has to be mentioned in a discussion about the pathologization of normal human male sexuality. I'm also generalizing (some men are gay, some men are true pedophiles, some men are asexual and I'm sure that there must be men who prefer middle-aged or elderly women), but even if men who preferred girls and women of reproductive age were in the minority their subjective preference would be the one that matches the actual biological function of maleness. I am not making an appeal to nature or arguing that age-gap relationships and an older male attraction to younger women are morally acceptable and good for this reason, only that such an attraction is completely 'natural' and to be expected. True pedophilia, homosexuality, asexuality and even a male preference for orgasm through something other than vaginal intercourse can meaningfully be considered 'deviant,' which is not to say that they are bad, unhealthy or unnatural; only that they are inherently maladaptive. Not all men prefer girls and women of reproductive age but the subjective preference for a partner you cannot reproduce with is matter-of-factly mismatched with the biological function of maleness/sperm production.
From an evolutionary perspective, the point of sex is reproduction; in the same way that we can eat for pleasure or for whatever purposes but, biologically, the function of eating is to provide the body with nourishment. Nature has no conscious agenda or goal but we normally have no problem talking about 'the function of white blood cells' or 'the function of the liver' to explain biological systems and the adaptations that led to the propagation of certain features.
It's not lost on me that male conventional sexual attractiveness also declines with age but the harshest condemnation of older people who either pursue or have relationships with younger people or don't flat-out lie about feeling attracted to them tends to be toward men (this might be changing, not in that the stigma around age-gap relationships is lessening; I think it's getting worse, but in that older women are more likely to be critiqued for being with the people who make them happy). From what I've read, male sperm quality peaks at 30 and declines at 35; a decade after female egg quality begins to decline. I would imagine that women generally prefer young men but, if conventional attractiveness is more or less rooted in traits that indicate health and fertility I think we should expect men (or even just gynosexuals) to have a stronger preference for young partners. There is a severe decline in male fertility after 50 (and advanced paternal age is associated with a higher risk in certain pregnancy complications as well as health problems in the baby) but it's not remarkable for men in their 50s and 60s to father healthy children. The oldest confirmed known woman to have a natural pregnancy was in her late 50s, the oldest known man to father a biological child was in his 90s (many doctors won't even perform IVF services for women over 50 because they are such high-risk pregnancies).
Sexuality as inherently damaging to adolescents
Another way the denial of human biology expresses, I would argue, is in the idea that sex for adolescents is inherently high-risk or traumatizing for fundamentally age-related reasons. I don't believe that prepubescent children are generally asexual (babies have been observed in and out of the womb masturbating, at as early as 28 weeks. I suspect most people would admit to having had sexual feelings or crushes as early as 6 or 7, many claim to have had them even earlier. Andrenarche might play a role in child sexuality, I'm not sure if this typically occurs two years before puberty or at 6 for most people. Small amounts of testosterone and estrogen in infancy might even explain infant masturbation, I don't know), although I won't claim that they have the fully-developed libido of typical adolescents, but it's clear to me that their bodies aren't physiologically wired; at the moment, to reproduce (if I'm not mistaken, vaginal lubrication doesn't typically appear until around 6-12 months before menarche) so I could at least understand the idea when applied to them (not being 'ready' for sex). Still, I don't necessarily see a problem with softcore erotic intimacy (maybe not vaginal intercourse) or a sexless romantic relationship between adults and prepubescent children. I can't understand the assumption of fundamentally age-related non-sociogenic harm (i.e. emotional distress that doesn't stem from having internalized the cultural idea that at-the-time-desired sexual intimacy with an adult as a child was exploitative and abusive) when it comes to adolescents. If your body produces sperm or has a menstrual cycle/ovulates it is, in a manner of speaking, trying to get you to reproduce. It's hard to imagine how natural selection would have favored a species that found sex traumatizing at the most fertile period in their lives (to go back to my point about fertility and attraction, it could be that a young woman in her late teens/early twenties and an older man in his early 30s are, other factors being equal, the most reproductively viable age-gender match).
In truth, the concept of asexuality only makes sense to me if it deals with a lack of sexual attraction and if we can differentiate that from libido, but if we're talking about the lack of a basic libido I would think that the absence of that or sexual instincts in males and females who are sexually developed enough to be capable of ejaculation and menstruation is likely a symptom of high stress, sleep deprivation or some medical issue (that would include problems brought on by some medications, like SSRIs. I'm not questioning people who claim to have not experienced sexual attraction or a libido to date, I'm just considering what might cause that since there are no hormonal differences between post-pubescent asexual adults and post-pubescent allosexual adults). Sex is a biological function and if your body produces sperm or menstruates it is 'designed' and wired to mate. If sex isn't inherently traumatizing for adolescents with similarly aged peers I don't see why it would necessarily become so with an older partner.
Who is an adult?
Lastly, I think our understanding of adulthood is also far removed from actual human biology. Contrary to popular belief, 25 is not the standard age for a final and complete brain development. This myth apparently comes from a 10-year longitudinal study carried out by Jay Giedd who assumed that changes in the prefrontal cortex that he observed in subjects (the oldest being 21 at the end of the study) would finalize by 25 (maybe because 25 is generally thought to mark the beginning of general decline) but later research has shown prefrontal cortex development to occur long before 25 and well into one's 30s. There is no evidence for any kind of brain development peaking at 25 or finalizing by then and no conclusive link between prefrontal cortex development and observable behavior (i.e. indicating cognitive maturity or impulse control) has been demonstrated, apparently even Laurence Steinberg; whose research has contributed to the myth, has admitted that he doesn't know where the idea of 25 as a notable milestone came from.
If we want to, we can choose to define the word 'adult' as a fully-developed human being but this doesn't describe an essentialist difference between children and adults (a still-growing teenager at 6 feet in height is taller than a 5'6 fully grown man in his 30s, potentiality doesn't tell us what a thing is currently) and, in a sense, we are always 'developing.' 'Growth' and 'development' seem to imply that changes are positive but living organisms exist in a constant state of change. Our 'full potential' is death. I don't think that we can avoid arbitrary lines when it comes to determining adulthood but I think that a coherent understanding of it, the least arbitrary one that I can think of, must ultimately be rooted in sexual maturity, the standard we seem to use for every other species. We could base this on a individual case-by-case basis (which seems to undermine the concept of noting age-related differences in maturity; identical twins could mature at different rates), or we could base this on the age at which menarche/semenarche or Tanner stage 5 would be considered delayed or abnormal (this will be gendered since the rule seems to be that male milestones occur a year after their female equivalent, or we could ignore gender differences and use the male standard to be cautious about assigning adult status too early on. I wonder if this is where the idea of 18 as the age of adulthood might come from, because Tanner stage 5 in boys might be considered delayed if it hasn't occurred by 18). I think we can draw a sharper line between people who have, or have had, an actually functioning reproductive system (even if it malfunctions in terms of various fertility problems) and people who don't yet produce sperm or have a menstrual cycle due to age-related immaturity than we can between people who produce sperm or menstruate without being fully post-pubescent and people who are fully post-pubescent.
*AMSC means 'adult-minor sexual contact.' I edited the title because I was afraid that my post was being censored.