I think it’s reductive because, IMO, women have spent decades fighting against objectification and essentially being seen as “just a pair of tits.”
Why then would we take the approach that actually, we’re just adult human females. Just a uterus, that’s me. That’s not all we have in common, and it’s not the end of the definition of woman. I don’t actually want to be defined by having a womb.
Sex absolutely exists, and is a biological fact, but it’s not the start and end of who we are.
The reason it’s difficult to find common ground in gender identity is because it’s different across different groups, but actually I think that’s right.
I’m not in the same group as every woman ever, because we happen to share biological fact, we’ve had different lives, different experiences and live in different bodies.
Woman isn’t universal, because how can it possibly be. I’m not the same as an Afghan woman, any woman of colour, any lesbian, any biological mother.
If society uses the biological fact of female to oppress women, through socially constructed gender stereotypes, it’s being classified by sex we should be rejecting, refuse to be limited because you happen to have certain chromosomes.