And so, by that reasoning, the sex offender registry doesn't actually prevent anything. You may as well say that we should do away with it.
The bathroom laws make it so obvious males CAN'T be in the women's legally. Many of the folks who "identify" as the opposite gender are still quite obviously of their original gender. The disguise thing only works if it doesn't matter that they are obviously male. You'd be VERY hard-pressed to show someone who ISN'T obviously male who IS a peeper/rapist. This law gives women the opportunity to identify when a male is where he shouldn't be and empowers these women to seek law enforcement protection. Just like the sex offender registry empowers the community to know and be watchful of the sex offender living near them.
I, for one, believe these laws DO work at preventing victimization. Even if it would only prevent one victim (like Megan), then isn't it worth a little inconvenience to small minority?
I will concede this: The law should not be based on birth gender, but on what equipment a person is currently packing. In the prisons, if you have a p**is, you go to the men's. No amount of crying and pleading deters them. If a transgender has had the surgery to remove their p**is (the creation of a va**na is a multiple surgery process), then I would say they are absolutely welcome to use the women's.