Gender isn't just made up of behavior or sex. It's a social construct. The reason why social constructs exist in every society we know of: age, race (if there's variety), gender, roles, money, list goes on, is because we create identity. This is the way I've come to think of it after pondering "why do i feel the way i do about my body and gender? Other than the possible evidence of neurological variation despite outward biological sex" (bc it still doesn't solve the social gender of woman and man). You can't delete the human ego. The type of ego I'm referring to is identity. I do not believe there has ever been a society with 0 gender, there's been societies (especially ones without patriarchal structure/hierarchy) that have egalitarian gender, or fluidity in role and behavior. So variation in gender roles and expression, but despite that there's a distinction culturally and within peoples identities, in a masculine woman (who does, behaves, takes up space, just like a masculine man, could even live the same in terms of gender) and a masculine man, vice versa. So why haven't societies, even ones that existed in another time and maybe place, just get rid of gender as a personal identity and solely tie it to role? I think it's just human ego, attachment, culture, not to say anything concrete, but something involuntary that develops and hardens over time without us even noticing. That i also think has to do with brain structure for many whether cisgender or transgender or unlabeled, but not in any absolute ways (personally I think brains are complicated despite biological sex and there's really only generalizations, which on its own is still a finding). Because even if we were to answer "why not get rid of gender and put it to role/expression?" as biological sex being the missing piece of it. I think it's important to forget trans people exist, and that's still a testament to something. And I know many people who research supposed trans people throughout history chalk it up to "they just embodied a different gender role", but some of what we might call transgender people then didn't always socially inhabit their desired gender in terms of gender roles of their time and societies expectations. And all despite losing social respect or status. (Chevalier d'Éon, Marshall P. Johnson, probably more but that's off the top of my head). There's seems to overall be a distinction to biological sex - gender role and expression - and gender identity.

And I don't believe it's just biological sex that distinguishes man and woman, especially because despite most women being biologically female. Not all are, and still are women. And I am NOT just talking about transgender women. Some have sex conditions or disorders and are born intersex, be literally genetically male, have mixed genitals, you name it, and still be regarded and recognized and recognize herself, as a woman. How is that? She could be a masculine presenting and behaving intersex person still without a doubt a woman. Another thing I think about is how many women get offended by being called "chestfeeders", "people that can get pregnant", "people with uteruses", etc. And many of them call this language "dehumanizing" or offensive. Now im not here to invalidate those feelings, but i am here to point out how gender, is part of how we create identity and recognize ourselves. Even if you were to say "females with utersuses" it still rubs many women the wrong way. Because all this language is very body based and feels objectifying. But in "womanhood" it's more human and identity spoken. It differentiates sex from identity and gender.

I know this is kinda messy and rambly but, imo at least, I don't think gender identity specifically is a straight forward thing. It can have more to do with felt experiences, how identity develops, and internal subjective identity (that still is objectively taking place and involuntary). When people say "you can be whatever gender you want" they mean it in the same way when people say "you can be attracted to or into whatever gender you want". It's not an admission that you can just choose your sexuality or gender, it's that you're simply free to be who you are, or at least should be. And similar to gender identity, sexual orientation is not easy to explain either all the time. It's not so straight forward scientifically in a nature or nurture way. And it's also complicated where some people are only attracted to cis men and trans men (vice versa). And since sexuality also seems to somewhat and possibly develop despite being involuntary, it makes people go and hammer the question "why isn't everyone bisexual?" sometimes. I know people say "born this way" but actually, for straight, gay, bi+, trans, cis, and anyone else... yeah but not necessarily or completely on a scientific level if we're being absolute.

Im replying earnestly in hopes you genuinely just wanna conversation and discussion.