I don't know a lot of openly gay people, but one of my former co-workers had been married and had children. It's possible that in a world without closets, fewer gay men would get married and have children. I wouldn't bet either way on the outcome.
One thing y'all may be overlooking is that relatively few homosexuals are exclusively homosexual. I've only known a few gay folks in my lifetime, and generally they were bisexual with a strong, though not exclusive, tendency toward attraction to members of their own sex.