Those arguing about molestation are stupid. A molester is going to molest, they aren't going to stop at the door and say "uh oh this is a girl's restroom I planned on molesting a little girl today, but that room is clearly marked girls only , so I won't be going in there"
That's just stupid.
The REAL argument is this.
I shouldn't have to worry that my child is going to see someone of the opposite sex exposed when using a public bathroom simply to make a few weirdos feel comfortable. I'm not comfortable allowing that, and I have just been told that my comfort is not as important as another person's.
And those screaming about civil rights can just shut the **** right up. You don't have a civic right to pee in the wrong bathroom, and no matter how much surgery you get it will always be the wrong bathroom.
But ultimately, the solution is a third bathroom marked "non gender"