I've already played games where that has been the case. I'm pretty anti- gay men, (if you want my thoughts on the subject of homosexuality some of the back messages are probably still around. The specifics have little to do with this discussion however) however) but that doesn't mean I get into some kind of frothing rage at the merest mention of gay men or whatever.
To be honest with most video games out there are set up, the only way the protaganist's sexual orientation is going to matter is if they go out of the way to bring it to the forefront. If this means that playing a game where the protaganist gets involved in numerous make out sessions with guys, or makes a big deal about being gay, is not going to appeal to me. After all that kind of thing is hardly a turn on for me, and since I don't like it, there is no real appeal to the situation, if they are going to put that much focus on it for the point of the game, my time would better be spent playing a game where this wasn't the case.
As far as games I've played with gay main characters or protaganists (that weren't me being a perv with a couple of girl characters) there have been a few. "Phantasmagoria II: A Puzzle Of The Flesh" involves an entire subplot about the character you control dealing with their homosexuality in their shrink's office. Then of course there is "Enchanted Arms" where the hero's main sidekick is a male homosexual with a crush on him. Then we have "Persona 4" where one of the party members being a gay man is actually the theme of a whole dungeon section. When it comes to antagonists, let's just say that if you have ever played a game about Conan that has featured characters from the books, a few of them were "boy lovers". Conan was before political correctness when it was written, and while it was never a focus, Conan has a major amount of contempt for gays and "boy lovers", and while never descriptive a number of his enemies were supposed to have been weakened by such "civilized decadence". Of course in the video games they rarely even go as far as the stories (both canon, and very old non-canon) did, which wasn't very far. Like most heroes a lot of his enemies "almost get him" in one way or another (a trap or spell, if not a straight fight) so you really can't call them impotent (so to speak) for their orientation irregardless of what Conan might think.
If you want to get technical, I think this entire "question" is a bit less profound than you might have intended. To be honest homosexuals have been fairly well represented as far as gaming goes, you just have to understand your dealing with a tiny percentage of the population. Fair representation does not mean "equal time with the majority" simply that a group is not totally neglected simply for being what it is. That's why I have such an issue with political correctness, and preferred Bioware's approach to romances in the first "Dragon Age" game to the "everyone is bi-sexual" approach of the second one. Granted you don't see much homosexuality in games in general, but that's pretty much in keeping with the number of homosexuals in society. Such things are there if you look for them, and have been for a long time.
That said, if you were doing a game like "Duke Nukem" but with the protaganist being an agressively flamboyant homosexual (of whatever style) instead of a manly flamboyant heterosexual, I don't think it would find much of an audience. Humor or not, it's meant to be slightly risque in it's own way, and someone without those tendencies wouldn't wind up appreciating the eye candy so to speak. I don't think there is enough of an audience to really sustain it.
That's a somewhat informed opinion as well, because it's been tried. They released those "Cho Aniki" games which are a series of tongue-in-cheek platformers featuring gay musclemen. We've actually seen ports of a couple of the titles to the US. From what I've heard the series has largely survived due to being relatively cheap to produce and a fan
base that is dedicated if not exactly numerous which does make it profitable. If it was tried on a fairly big-budget level like "Duke Nukem Forever" I don't think the audience would sustain it since there just wouldn't be enough gays with enough interest, and even if homosexuality doesn't offend someone they really aren't going to find a lot of gay innuendos aand cheesecake all that thrilling to want to dedicate hours upon hours expoising themselves to it, after dishing out a $60 price of admission.
Such are my thoughts. Due to being an admitted perv I'm intentionally staying away from the idea of lesbian characters because hey, like a lot of guys, I do find that fairly "hot" when presented the right way. Also I do believe that gays and lesbians are differant situations entirely, but that's not something I'm going to go into again. Again there are probably some back messages where I explain it (and the likely arguement would go nowhere) but simply put it has nothing to really do with it being "okay because it turns me on". The point being that I more or less agree with you excluding that aspect of the discussion. Especially seeing as I think that there are enough people out there like me in their "interests" irregardless of why that a hot lesbian heroine can find a niche among the male video gaming population and be sustained at a fairly high level, where I don't think gay men can be. You could probably do a Lesbian version of Duke Nukem and all the guys who bought Duke Nukem would also buy that game for largely the same reasons, and wind up appreciating the eye candy just as much. Whether it's fair or right or not is not something I'm going to argue, it just is, which is why (as I said) I agree with you there.