(apologies in advance for the long reply; this is meant to be a genuine, good-faith attempt to explain so i hope my language doesn't sound too harsh!)
i think the simplest way to explain this is to say that there are two ways to describe the meaning of any given word: colloquial and personal.
(and i will say that this isn't the exact definition of colloquial, but it's the best word i can come up with for this phenomenon)
colloquial meanings are meanings that we use in every day, casual language. for example, the colloquial meaning of lesbian is woman who loves women, the colloquial meaning of gay can either be man who loves men or anyone who isn't straight, the colloquial meaning of trans is someone who doesn't identify with their AGAB, so on and so forth.
colloquial meanings aren't really something that can be easily changed, because they're based on common layman knowledge. you'd have to influence a large majority of the population to change a colloquial meaning of a word, and in general, people identifying with a label will be judged by the colloquial meaning first and foremost. this isn't necessarily a bad thing! that base understanding is what allows labels to be useful in the first place; it's a short way to define any part of your identity.
personal meanings, on the other hand, are the crucial part of this discussion, and they can be a lot more complex. personal meanings are what any label means to the specific individual using it.
no one experiences a label the exact same way (for example, an aromantic homosexual woman and a homoromantic asexual woman would both be considered lesbians,) so while the colloquial meaning gives you the basic idea, personal meanings often require more explanation. that's why pretty much all labels are umbrella terms!
this is especially important because, for example, labels very often change over time, so you'll find people identifying with terms that were perfectly fine when they were young, but are now considered offensive or outdated (elder queers referring to themselves as transexual, for example).
just as well, when it comes to personal meanings, the finite borders that colloquial meanings define become...blurry. gender and sexuality very often messy, contradictory experiencesāespecially when you, for example, spend a long time as a lesbian and in the lesbian community, only to realize that you're transmasc, or bisexual, or both a woman and a man, or sometimes a woman and sometimes a man, and so on!
this is a quote i used in my very long post about mspec lesbians that i think explains my point well:
ā10 years ago when I left my husband and full-time role of motherhood, it didnāt make me less conscious of what being a mother means. In fact, it gave me a deeper understanding. I am still a mother. That experience cannot be taken away from me. In much the same way, my lesbian awareness isnāt lost now that I claim my bisexuality.Ā When I realized my woman-loving-woman feelings, and came out as a lesbian, I had no heterosexual privilege; yet there were important males in my life, including a son. I am bisexual because itās real for me, not in order to acquire or flaunt the privilege that is inherent in being with men.Ā My political consciousness is lesbian but my lifestyle is bisexual.Ā If I keep myself quiet for anotherās sense of pride and liberation, it is at the cost of my own which isnāt healthyāemotionally, politically or medically.Ā Not only is it unhealthy, itās ineffective.ā
āLani Kaahumanu, āBisexuality & Discrimination,ā BBWN Vol. 3, No. 6, Dec 1985-Jan 1986; Reprinted from the 1985 Gay Pride March magazine, San Francisco
when you realize a label doesn't fit you anymore, especially after years of identifying with it and interacting with that community, those experiences don't just shed off like a loose skin. they stick with you! that's a big reason why you'll find people still identifying with, for example, the lesbian label and community, even after they've taken on a "contradictory" label.
this is only one example of why someone would branch outside of the colloquial meaning, but bringing up any example is important, because it leads me to this: personal meanings largely do not influence colloquial meanings.
THAT'S why people tend to have this issue with people who don't fit the colloquial meaning of a word! personal meanings aren't really respected or even thought about, and the assumption is generally that people are trying to change the colloquial meaning because of their lived experiences with the label.
if i were to say "i am gay (in the sense of mlm) and i am primarily a girl", people would assume that i'm trying to say that the colloquial meaning of gay should be "anyone who is attracted to men", which is not what i am trying to do. i am saying that my personal experience with gayness is influenced by the fact that, while i am primarily a girl, i am also a man, and also nonbinary, all at the same time.
that said, it is VERY DIFFICULT to change the colloquial meaning of a word via one's personal meaning! it would take an entire movement to change the colloquial meaning of a word, and even then, there will always be dissent and disagreement on the changes being pushed forward.
basically, what i'm pushing for, at the very least, is not a complete overhaul of the colloquial meaning of any word. people are always going to use labels as a way to quickly understand someone's identity, and colloquial meanings are needed for that.
what i am pushing for, however, is respect for personal meanings. each person's lived experiences with labels and being lgbtq is incredibly important! it's what makes this community vibrant and beautiful! to put it upon yourself to decide which words any particular person can identify with is to enforce the same rules that bigots use to put us in boxes, and, if i'm being completely honest, it often shows an extreme lack of understanding of queer history.
there are some really big lesbian projects and communities that explicitly include trans men and bisexuals. this includes the boston dyke march, stated right on their facebook page:
"The Boston Dyke March is a non-commercial, community-centered, grassroots, inclusive pride event. Our organization is for everyone: Dykes, Lesbians, Queers, Bi-Folks, Trans women, Trans men, Genderqueers, Non-Binary Folks, Allies, and everyone in between."
likewise, the lesbian bar project states this on their main page:
"We believe what makes a bar uniquely Lesbian is its prioritization of creating space for people of marginalized genders; including women, non-binary folks, and trans men. As these spaces aim to be inclusive of all individuals across the diverse LGBTQIA+ community, the label Lesbian belongs to all people who feel that it empowers them."
another note that i feel often goes unsaid is that the lesbian community has had a positive relationship with masculinity for longer than exclusionists and radfems would like to admit, in the form of butches! butch lesbians have been around since the 1940s-50s, and even as the lesbian feminist movement decried butches as "inextricably misogynist and butch-femme relationships as dangerous replications of heteronormative roles", butches have gone strong and heralded lesbian masculinity for decadesāmore than just through presentation. here's a quote from the renegades by kerry manders:
"And while there remains some truth to butch stereotypes ā give us a plaid flannel shirt any day of the week ā that once-static portrait falls apart under scrutiny and reflection. Not every butch has short hair, can change a tire, desires a femme. Some butches are bottoms. Some butches are bi. Some butches are boys."
this is also a really good article about the line between being a butch lesbian and a trans man! i would select a specific quote, but i honestly really like the entire discussion here, so i highly suggest you read it :)
i've been writing for about... an hour and a half? but i hope this makes sense! basically:
people are always going to assume labels mean certain things, and this is fine and makes communication a lot easier
however, individuals will often have lived experiences with certain labels that deviate from the colloquial meaning without necessarily changing it
this personal meaning is what makes the lgbtq community diverse and special, and to put rigid boundaries on personal meanings is to enforce the same rules that bigots do
there are some very big lesbian projects that explicitly include trans men and bisexuals, such as the boston dyke march and the lesbian bar project
lesbianism has also always had a positive relationship with masculinity through butches, and likewise there's a lot of complexity in the line between butch lesbian and trans man
i've been writing this for so long goodness gracious
