I’m afraid that if we don’t get single-sex spaces back soon, we never will.  Allowing men into women’s prisons and locker rooms is still a weird, new (“cruel and unusual,” if you will) idea and can be opposed on those grounds.  If we let male presence in spaces where women are undressing and/or vulnerable become the norm, and stay the norm for very long, single-sex spaces will be the “new” idea and our only arguments will be that single-sex spaces benefit women, which no one cares about.  There will never be money on our side, either. 

 so much for the Geneva Convention, eh? 

 To get some of the money on our side, boycott all businesses with mixed-sex multi-stall restrooms and changing rooms: YMCA, restaurants, coffee shops... Once we notice it, we send a complaint in writing and never return. That at least matters to them.