Now, that argument can be turned around: Why wouldn't you choose a normal orientation for your child if you could??
But... I agree with the comment above... in a "gay-less" society, it's going to be tough to find a good hair-dresser, or purchase a well-fitted suit. And, our church choir will be short of tenors, too! :-O
My other theory is that it's a kind of population control, considering they appear more in urban areas and are so drawn to occupations of service (again- like hive workers or ant colony slaves). Their job, stereotypically, is to make others happy- but not to labor and do things that would expand our population...
One test for this would be to drop colonists off in the wilderness - where they have to fight for survival - and see long the gays remain active. Such a community wants nothing to do with them; homophobia is nature's method of discouraging gayness and decadence, which are bad traits for a struggling colony.