Unisex bathroom

I'm currently doing research at the Kent History and Library Centre in Maidstone. It's a fairly new building that combines the library with the county archives. To my surprise, the bathroom there is unisex. As I walked inside, I wondered how such a place would go over in the states. Not well, I imagined. But why?

I thought it might have something to do with the actual construction of the bathrooms. In the states, the bathroom stalls are simple metal dividers. There are usually pretty big gaps between the segments and the doors end several inches above the floor. I'm speaking of the ladies' rooms, obviously, but I know the men's rooms aren't much different. In Britain, the individual stalls are more like small rooms. You have a proper door and solid walls. You have actual privacy. No one sees your feet with your jeans gathered around your ankles. And this privacy, I thought, made it easier to have unisex bathrooms.

When I visited the loo later, however, a man entered right behind me and I felt uncomfortable. I was totally creeped out by the fact that a guy was in the same bathroom as me. When I went to wash my hands, an elderly gentleman was there washing his. I had a renewed rush of the creeps. 

Clearly, the solid walls and doors gave me privacy, but they did nothing to quell my need to be in a ladies-only bathroom. Now I'm trying to figure out why. How has the separation of men's and women's public bathrooms crept into the American psyche? Is it just American? Were those British men as creeped out as I was? 

Things that make you go hmm.