http://www.nytimes.com/2015/09/02/us/teenagers-protest-a-transgender-students-use-of-the-girls-bathroom.html?_r=0
If you cannot set boundaries, then your ability to say no erodes. A boy with a penis going into a girls changing area is simply unacceptable. It is a “hostile” environment, to use the term they would use if they were trying to demonstrate sexual harassment.
But the Left does not truly believe in anything but cultural destruction, so they are quite content to contradict themselves regularly. They don’t see the contradictions because that would require the disciplined use of logic and principle, and if they were capable of either they would not be Leftists.