Thank you for a thoughtful and interesting response. I am going to attempt to reply similarly.
I would like to start with the idea that "sex" and "gender" are two entirely different phenomena, and that gender is a social construct with no innate or natural origins. This seems like an almost too-obvious statement to make, but I think it's an important statement to begin with in order to understand my entire argument.
Another question I think is relevant is, "if gender is a social construct, why and how did it evolve?" The current understanding of this is predicated on the idea that, while gender and sex are known to be separate today, they were historically and traditionally connected. Allow me to further explain (it's a long explanation, but I promise I have a point).
In nature, female mammals have a lot of control over reproduction. This is commonly referred to as "sexual selection." Because females actually *have* their species' babies, their choice in which males to reproduce with has significant implications for evolution. It is also a power that they have over males. This was also true of early humans - women (adult female humans - this was before gender) had the power to decide which men (adult male humans - again, before gender) to reproduce with. But anthropologists theorize that with the development of agriculture, and therefore the development of concepts of "property" and "labor" and "economic surplus," it became beneficial for a community to have more children in order to produce greater economic output and achieve more wealth. As society was evolving, it was encouraging women to have many children -- and, for efficiency, be in charge of raising them. The concept of "marriage" also came out of this, because men wanted to know which children were "theirs" in order to pass on intergenerational resources. So, we see the development of marriage *and* gender roles (aka women raising children), which were of course the beginnings of patriarchy. With this new system of marriage and sex-based roles, men had control of economic output and therefore women's livelihood. This BBC article has more information if you're interested: https://www.bbc.com/future/article/20230525-how-did-patriarchy-actually-begin.
To summarize, the origins of women's oppression is based on biological sex. If we did not have the ability to bear children, patriarchy might not have even existed. Gender wouldn't exist, either, because there would be nothing to pressure us into the role of "raising children." Gender and sex are separate, but they have always been connected. Gender, in fact, exists *because* of biological sex.
Lastly, it's important to note that gender has evolved into something that is not neutral. I've heard many people describe gender as a "spectrum." But I don't think that's entirely accurate. It's more of a hierarchy. Think about it - how much time, energy, money, and mental attention goes into performing femininity? The makeup, the clothes, the aesthetics, the hair removal, the body improvements…and that’s just to *look* feminine. You also are expected to be the caretakers of your house and your family, which is so much mental and physical energy. Meanwhile masculinity is all about neutrality. Sure they have some pressure to look good, but what do men’s routines look like? Are they as involved as women’s? Do they spend as much time and money as women do just to look presentable? Or are their standards much more relaxed? Also, what do masculine behavior expectations look like? I think it’s safe to say that masculinity and femininity are not neutral - performing femininity puts you at a disadvantage by design (economically, socially, and physically). Gender is a hierarchy that evolved as a tool of women's oppression.
With that understanding of sex and gender, I'd like to respond directly to you now.
You begin your post by posing the question, "are trans people their assigned sex or their identified gender?" For all intents and purposes, the answer is both. A trans man is a female who identifies as the male gender. A trans woman is a male who identifies as the feminine gender. A nonbinary person can be either male or female, but they identify "in-between genders" or however it's described. You get the idea. This is why it's important to bring up intersectionality - we cannot pick and choose which aspects of our identities matter when discussing oppression. We are everything all at once.
You also bring up the term "gender ideology" and argue that it's not a real term. I disagree. The definition of "ideology" is "a set of doctrines or beliefs that are shared by the members of a social group or that form the basis of a political, economic, or other system." Therefore, with "gender" serving as an adjective in the term "gender ideology," that would make the definition of gender ideology, "beliefs about gender that are shared by members of a social group that forms the basis of a political system (aka patriarchy)." Isn't that objectively the best way to describe your beliefs? You believe that "gender" is a social construct that describes how people should act/think/behave. This informs your politics, because you also believe that the best way to liberate people from the patriarchy is to allow people to choose which gender to identify as instead of assigning people a role in society based on their sex. I truly think "gender ideology" is a perfect term to describe this. Is your point that some people who disagree with you also use the term in a more derogatory way? If so, respectfully, who cares? You can use the same term in a positive way and it wouldn't be any less accurate. In turn, I belong to a "gender-critical" ideology. It's just what those words mean. What are your thoughts?
At one point you mention that the original post is about gender-based hatred. The post definitely mentions hatred - specifically, hatred from "trans exclusionary radical feminists." If both are true, do you and the OP believe that "terfs" hate trans women because of their gender identity? If so, as a gender-critical feminist myself, I feel the need to point out that this is inaccurate. First things first, even the term "trans exclusionary radical feminist" does not reflect what we believe. We prioritize the female sex and liberating female humans from oppression. That means we do not exclude all people who identify as transgender, because we still want to liberate a female who identifies as a man. We do, however, exclude males who identify as women. And that was the point of my reply - many gender-critical feminists do feel frustration and hatred towards males because they are our oppressors. We do not write those "hate posts" because we think it's weird or unnatural or whatever for a male to perform femininity. We write posts that criticize trans-identified males because we do not think that their behavior aligns with female liberation. Allow me to explain further.
I've already given the historical context for gender and how it is a hierarchy designed specifically to oppress women. Because of this, gender-critical feminists do not agree that allowing people to choose a gender to identify with is very progressive. Based on our gender-critical ideology and social analysis, we believe that by saying “womanhood is a feeling,” you’re perpetuating harmful stereotypes about how “true women” are “supposed to act/feel/think/behave.” We also believe that, in many ways, you’re reinforcing the system of gender by continuing to use it and making it a core part of your identity. We actually believe that it would be way more disruptive to patriarchy if someone were to break gender norms *while continuing to identify as their sex,* because it would show the world that gender is made up nonsense.
Gender-critical feminists also believe that gender-based definitions of words does a lot of harm, because it's eliminating language that is used to discuss real sex-based oppression that women face. By redefining “woman” to refer to gender (a harmful made up hierarchy) instead of sex, you make it impossible to talk about sex-based oppression without making it difficult to understand (not every “cervix owner” knows what a cervix is, especially English language learners) and dehumanizing (I am not the sum of my body parts, I am a woman).
So, while the intentions of the post might have been to comment on gender-based hatred, it also thoroughly misunderstands the core disagreements between liberal feminists and radical feminists. Biological sex is more relevant in this context.
And speaking of biological sex, it's also relevant when discussing the oppression of trans-identified individuals. You mention examples in which a "perfectly passing" trans woman might still experience oppression.
Firstly, I have never seen a perfectly passing trans woman in person. I think that's because secondary sex characteristics are present in a lot of physical development, and so they're hard to completely eliminate (particularly if the individual is a trans-identified male). I'd say it's very rare, if not impossible, for a trans-identified male to perfectly pass. But I digress, that's not super relevant anyway.
Secondly, my point is that these trans-identified males still benefit from male privilege. Your counterexamples are all gender-based, but perfectly-passing trans women still benefit from sex-based privilege. For example, they will never have to worry about abortion access. It's irrelevant to their bodies. They will never have to worry about the social stigma of getting their periods, or of female-specific conditions of PCOS being under-researched. You bring up seatbelts, but one key component of seatbelt testing is height. Seatbelts are tested for the average male height, and trans women cannot change how tall they are. Same thing with trans men - they are female. They will still have to worry about abortion access and periods and female-specific medical conditions. They still have to worry about being too short for seatbelt protection.
Socialization is also a factor, here. That is a grey area between gender and sex. Because, unless otherwise identified, children are socialized based on their sex. So trans-identified males still benefit from male socialization. They are taught to be more confident, take up more space, be assertive, and more social behaviors that are supposed to help them become dominant over women. That doesn't just go away because of a gender identity change.
Thirdly, I wonder about those examples of gender-based oppression that you bring up. Is gender the only lens in which to analyze these disadvantages? I see them differently. Let's look at trans women's increased risk of violence. First of all, we know which sex is more likely to be violent, right? It's males, statistically. So this risk is, more specifically, that males will harm these trans-identified males. And I think it might go deeper than "it's because they're trans." I think it might be because these violent men see trans women as 'feminine men.' These violent men see trans women as 'men who are breaking the code of masculinity and patriarchy.' It could even be interpreted as homophobia, because one common (wrong and harmful, but common nonetheless) stereotype is that feminine men are gay. But I think the violence might come from *reinforcing gender norms,* which in my mind is slightly different from "being trans."
One approach to solving this problem could be to normalize the idea that anyone can behave femininely despite their sex. And yes, that would probably, slowly, shift cultural attitudes away from a binary approach to femininity and masculinity and protect trans women from male violence. But it would also keep gender as a part of our society, and is that what's best for female humans? Is the goal to eliminate the binary to liberate women, or is the goal to liberate women to be free of a binary?
I outlined earlier that I don't think the strategy of "choosing your gender" is the best option, because gender, at its core, is harmful. I think that what would be best for everybody is to eliminate gender entirely. Abolishing gender would benefit women and females, and it would also solve trans women's increased risk of violence, because there would be *zero* expectations of how people are supposed to behave based on their sex. This is not to say that biological sex would become irrelevant -- obviously there are some things about biology that we can't change, like how human reproduction works and what secondary sex characteristics humans develop. So we can't eliminate sex. But we can eliminate gender. And I think that should be the ultimate goal.
This was lengthy. If you made it this far, thank you for your time.