Primarily, I'm for leaving things as is on current buildings because I don't see the cost of changing things to be justified in most cases. So this would all be related to new buildings/massive renovations already being undertaken for other reasons on current buildings.
As for why gendered as the default, I don't really see that unisex will solve all that many problems. People that have issues with trans* folks will have issues with trans* folks regardless of what the bathroom facilities are. Having no wall between you and the gender than is more likely to harass you (if that's a problem for you) is going to feel (and possibly be) safer with gendered facilites.
Also, I think in most places people with kids or are caregivers for someone of the opposite gender, there's generally few problems. I say this as someone who has lots of experience taking care of children.
Of course, there are parts of the world, societies and specific places where one will be significantly beneficial over the other. For example, if someone lives in a place where people are strange and take issue with parents bringing their kids into the opposite restroom (or going into the opposite restroom with them), unisex would be a better option. On the other hand, unisex bathrooms in the military (when I was in at least) would be severely problematic. There was more than enough problems with sexual harassment/stuff that goes beyond sexual harassment, and having unisex bathroom would have made things even worse.



Oh indeed. Yeah, no. On many, many levels this would be the worst idea ever.