People arguing against unisex bathrooms because of predators and rape should really look into college life (as in dorm life) and bathroom sharing.
In non-single sex colleges, the bathrooms are all unisex. Given that college students are more likely to be drunk and are highly promiscuous, you would think that perhaps sharing a unisex bathroom would increase the incident of rape and unwanted sexual assault. But nup, no such increases are seen. In fact the system is quite useful given that there are so many college students and not as many bathrooms, it enables flexibility for students to use any bathroom on the college campus. Surely, you can't still argue that unisex bathrooms open up and encourage rape.....
Besides the most popular argument remains in that if a law can't stop a rapist, a bathroom sign isn't gonna anything either.