How do you say which roles are homosexual, unless specifically stated?
What people are opposed to is the caricatures of gay actors played by heterosexual men. Like Robin Williams.
Let me explain. In Western tradition, comedy consists of not crushing. A straight man who plays a gay caricature is someone who is in power and who deliberately makes fun of someone who is not in power. In Western societies, this is perceived as being in bad taste, what crazies call "political correctness".
So, if you want an absurd movie about the caricature of a flamboyant gay man, you should hire a gay actor. If you want to portray a homosexual man in a drama or a "heterosexual" man in a comedy, you can easily start a heterosexual film without raising any real objections.
It's no different from what you play with rednecks for laughter, like with the Beverly Hillbillies or Hee Haw. An Asian who gets up and spends an hour saying, "You might be a redneck if …" will not be received in the same way as Jeff Foxworthy with his drawling voice from the south. Larry the Cable Guy played by a New Yorker would not be acceptable.
I realize that it is difficult for you, since the usual conservative idea of comedy is that insults and ethnic comedy on a large scale.