We have separate sex toilets in order to preserve peoples' sense of privacy and modesty from being an object of titillation for others, on the assumption that letting biological men be present when biological women are undressing, and vice versa, is always and solely going to offend against that. But surely a gay man in a womens' changing room is going to be unaffected by women changing around him..
Not really,
We have single sex spaces mainly because women and men have different biological functions, for example men stand up to pee. Women have periods.
I do not want urinals in my toilets, neither do I want male people pissing on the seats.
Also, how the hell am I supposed to know whether a man in the women's space is gay or not?
"Oh hi, I'm alright, I'm gay"
Next thing he slides his smartphone under your changing cubicle to film you against your knowledge.
Just, no. No males, men, gay, straight, transwomen, in women's spaces. We have women only for good reason, and any males in them at all for any reason stops them being women only.