Related are hospital exams. There are legal requirements staff have based on the sex of the patient. Changing sex to mean gender and then making gender whatever you want to list on your ID has legal ramifications on these people you can’t avoid so long as the government has a hand in them.
The solution is simple, really — all it takes is for everyone in the entire country to become a flawlessly rational philosopher-sage (like Brendon) and admit the self-evident fact that gender is a social construction and therefore there’s no logically defensible reason that female arrestees should object to patdowns by male cops, for example. Problem fixed!
I don’t doubt your personal sincerity, nor your intentions.
Keep talking to Brendon; sooner or later the nagging thought will cross your mind that he’s not a sincere trans-ally, but a right-wing troll trying to make the trans movement look as barkingly insane as possible. (I don’t think he’s really a right-wing troll; mostly he’s just a quasi-religious utopian whose views are as much grounded in real-world biology as faster-than-light Warp Drive is grounded in real-world physics. Probably harmless, though.)