It seems there are some people that can’t grasp that gender isn’t a fixed thing and it’s meaning varies between groups and cultures, and to some the possibility of a society where we don’t categorize based of gender OR sex seems infeasible but it’s certainly possible.

Once we allow gender freedom, get rid of sexism, and then the binary gender boxes will naturally slowly stretch out until they don’t exist anymore which at that point everyone already adjusted and didn’t lose anything. But in present I feel like trying to figure out a “science” to gender identity (a social construct that may be partially influenced by neurological factors, but also social/cultural factors) would just lead to more gatekeeping and we should just focus on trans/non-binary rights instead of brain science validation.