As is so often the case, this general statement is simply not true. Not ALL men are thinking about that next score. And, certainly, one cannot truly suggest that there are not some women out there that simply are thinking about making their next score...
Not all men, no. But there are enough to not have men and women sharing public toilets.
Well, that, to me, is not the best reason to say why unisex restrooms are a bad idea. And it does not address the fact that there are, indeed, sexually predatory women out there as well. It is not really fair to claim that the men would cause all the problems with such an arrangement.
As for public restrooms, if I were to design a building, I would put twice as many stalls in the women's restrooms as opposed to the number of urinals and stalls in the men's room. That would eliminate the long lines in most cases. Women, oftentimes, wear more complicated outfits than men do, as such take more time using said facilities even when the line is not a factor.
I do, however, agree that unisex restrooms/washrooms are generally not a good idea.