Galaxy
Because being gay is being attracted to someone of the same sex. So Eddie izzard for example cant be a lesbian because he is a man.
Absolutely.
Being gay means that there is an attraction to someone of the same sex (as you've just said, Galaxy!) and being straight means that you are attracted to the opposite sex. If sex is flexible, how does that work?
A gay woman is not attracted to men, and to suggest that she should be attracted to a man who says he is a woman is deeply offensive. It suggests that lesbians are women who just like the look of other women, as opposed to having a genuine sexual attraction to them. That is made worse when TRAs start to attack lesbians for refusing to entertain the idea of sleeping with untransitioned transwomen, saying that a penis is no different from a strap-on, and that they are bigoted, prejudiced, and all the things that people have been accused of on this very thread.