Even if you want to separate sex and gender and define sex using sexual characteristics (not actually a good idea, see works by Judith Butler and Julia Serano among others, although I wont fight that point here), almost no sexual characteristics are immutable. The only ones that I can think of are chromosomes and gametes, but chromosomes aren't even binary (or observable without a microscope) and gametes arent a good basis either -- should being infertile affect your sex?

[–] LifeInMultipleChoice@lemmy.dbzer0.com 1 points 1 day ago* (last edited 1 day ago)

Let me ask a genuine question then, if you don't separate sex and gender, how does one recognize things like differences in people's eyes. Our gender roles have no effect on those physical characteristics that are created by varying factors such as chromosomes. We characterize those differences into the area of sex normally, but like I said previously, there is overlap in the sexes, chromosomes aren't always in category A and B.

Or are you saying sex shouldn't exist at all as a classification? Fertility has no effect on what physically was attempted to be formed. Mutations and errors will always occur. That doesn't mean someone should be alloted lesser rights, that just means they formed differently.