I will try and chime in with a few points:
a) In Europe, we have all those laws about sexual violence, mobbing, and various other sex crimes. I'm pretty sure a (sex) man in a women's bathroom would be in for, like, a major fee and a few months in jail... Since law is the law, and common sense has no implication in the court. Also, really, if we are going to use common sense instead of billions of laws, I'm in for it, but we really need to get rid of, like, 85% of the laws already established.
b) I have no beef with unisex bathrooms one way or another (stalls/separate rooms/any other way). I've even worked in a place where all bathrooms were unisex (room kind), and it seemed to work well enough. I think bigger problem would be with the changing rooms/locker rooms in sporting establishments and schools - those are often open (I mean: no stalls/small rooms/any kind of separation), at least where I live; hardly a way to make them unisex without some major problems (high schools come to mind).
c) If we are really going to regulate transgender bathrooms, I postulate to regulate claustrophobic bathrooms (what is with those tiny, tiny stalls?) and germophobic bathrooms (all those people not disinfecting anything!) and... You catch my drift. This is not a mockery, mind you - in my country, we have gotten 26 000 pages of new laws... Last year. This is like 70 full-sized, A4 pages of text to read daily just to keep up with the law. And I do mean daily - including weekends, holidays and stuff. I don't think I know 5% of the laws in my country, and I'm pretty sure I couldn't even name all the felonies that could land me in jail, despite trying to keep up at least with that...