[Oni]

I kinda agree with @meow here, but at the same time, I don't think it is a black and white issue. If you can clearly tell beyond reasonable doubt that the person who claims to identify as say female is male than obviously they should not be allowed in.. with that said, if a bulk manly looking FtM was in the women's bathroom, I think the same people arguing for "go to the genitalia corresponding with your bathroom" would not be fans of big manly looking females with vaginas in there.

Sexuality could also be a question. I'd assume a lot of MtF are still heterosexual.