As one who has been to gaming conventions before, namely GenCon, in particular, I would guess one reason homosexuals would want their own con is so they don't have to be continuously assaulted with all the "that's gay!", "that's so gay!", "Gaaaaayyy!", and "you gay-ass noob!" type comments that gamers so casually and callously spew all the time in reference to something, anything, they don't like, think is wrong, or consider abominable. Imagine having your particular choice of lifestyle being used as a derogatory term or pejorative all the time. Eventually, no matter how you try to tolerate it, it will get under your skin and irritate.
It's similar to how some of us old-schoolers are very sensitive about the word "******" because it has a very particular, insulting, and degrading meaning to us due to the historical context through which some of us actually lived. Online gamers frequently toss the word around with reckless abandon; we can try to ignore it and move on, but, sometimes, after repeat exposure, it can begin to grate against the skin.
The heart of the problem, in my opinion, is the outright thoughtless and careless insensitivity of some gamers toward others, and the fact some gamers can be more ignorant, knuckle-dragging hate-mongers than anyone else I've ever seen.