Does it matter at all? Hell, I'd even play Gears of War if Marcus was having foursomes with Baird, Cole and Dom, as long as it didn't show anything and the game was still awesome. Homosexuality isn't a problem, it's simply a way of life, so why not play a game with a gay protagonist?
That said, it's interesting that although we've seen plenty of other media with gay protagonists (books, films, TV, even music, and so on), we've never seen a game so far with a gay protagonist. Japanese eroge doesn't count, by the way.