Changing the label doesn't change the logic. Transgendered people who can't handle using a restroom with other people of the same physical sex as themselves are just as phobic. Yet somehow that's ok, but the other isn't? Why?
There is nothing preventing that kid from using the boy's bathroom except his/her own fears and hangups. None at all. Yet, we're expected to require that everyone else set aside their hangups about sharing a restroom with someone of the opposite sex on hold because a very tiny percentage of the population feels uncomfortable the other way around? That makes no sense at all.
Well, it was the primary idea behind the founding of our country. Aside from that though, no big deal, I guess.
People who actively disagree with your sentiment:
Plato, John Adams, De Toqueville, Mill, Nitche, Aynn Rand, I'll just stop there, I guess.
The entire reason Law exists as a concept is to enforce the rights of minority actors. Even the ones you don't like.