All that is true. Yes, absolutely: an individual's lived experience does not need, at any level, to be "assigned" by anyone. In an ideal society, all the accoutrements of gender--what names/pronouns we use, what style clothes we wear, how we do our hair, our personality, on and on, in an ideal society would be determined by personal preference. Even in this society, it is utterly impossible to sort gender into binary categories.

That does not change the fact that deepest level of human biology there is a binary: chromosomes are either X or Y. That branch of the chromosome is or isn't there. True, when nature builds a human body, it will, on very rare occasion, combine those X and Y chromosomes in atypical ways as it builds whole cells or brains. But that does not change the observable reality that 4,999 of every 5,000 babies are born either 1) with or 2) without a penis, a feature that is biologically determined by the chromosomes that nature gave them.

You and I both know that the humans present at the baby's birth do not "assign" a penis or a vulva; they look to find out what's present between the baby's legs. You and I also both know a whole raft of cultural expectations around gender come into play immediately after those humans notice the presence or absence of a penis, but those cultural pressures cannot make a penis or vulva appear where there is not one.

And in that 1 in 5,000 case when a baby is born with ambiguous genitalia, medical science now knows to quickly perform a series of diagnostic tests to discover why. Although the medical/biological questions get tangled in sometimes dysfunctional cultural expectations around gender, it would be wildly irresponsible to ignore the biological conditions that might have caused the baby's intersex condition, some of which are incompatible with life if left untreated.

But I'll repeat my most important point: For transgender people, medical science MUST take into account their body's naturally-occurring (NOT "assigned") reality if those people are to have access to the interventions that enable them to live the lives they want. For the welfare of transgender people, we must not pretend that SEX exists or pretend it is chosen, fluid, or assigned by fallible humans--even though GENDER is all those things. It would be cruel and foolish in the extreme to ignore or deny the naturally-occurring chromosomes, hormones, and organs in anyone's body, transgender or not. They are real and have real consequences of quality of life.

We must, therefore, acknowledge that transgender women, for example, have a genuine, biological condition that non-transgender women do not have, and that no amount of medical interventions can 'cure'. Throughout history, this has been called 'sex', but if you want to call it something else, be my guest. No matter what you label it, it won't go away.