So, obviously, people don’t generally change their legal gender for an advantage somewhere. But if they do, that’s a pretty good sign, not that it’s too easy to change your gender, but that there’s a gender bias in the law.
So arguably, the easier it is to change your legal gender, the less of a problem gender-based affirmative action is. Conservatives must love this! End liberal overreach in one easy step!
The “spandrel hypothesis” is the front runner explanation. Essentially we didn’t evolve to have chins but rather evolved other things that are helpful, and the chin is a byproduct of that other evolution. Not harmful so it didn’t get selected away, but not helpful.