Okay, it seems like there is something to what you are saying about the motivation here. What about gay people in showers though? They are the correct gender, but could have the same motivation as this person for showering in a public locker room. Is the problem here that they are a man showering in the women's room, or any person showering in the room with a sexual motivation?

To me this is about expectation. I expect in a mens shower, that no women would be there, but would make no such assumptions about a gay person not being in the shower.