Most likely, when populations get out of hand in the future, they'll probably have enforced sterility by lottery, or some other fair means to ensure population control... and that would add a whole slew of new social issues to contend with... and frankly, sexual preference would have no impact on this, as people could always sell their semen / eggs... See? Still not a gender preference issue, but an economic one.
Also, since people won't willingly give up sex, sterilization may be the only option other than starvation or disease -_-'...
Anyways, in a society like that of Star Trek, where beings of different species are having children, would homosexuality really be any issue at all?
Also, it's only after monotheistic religions like Christianity popped up that homosexuality was truly castigated in our own history... In some ancient Greek city-states, not only was homosexuality common, but between 'beared older men' and 'younger beardless youths'! Zeus had a pretty young candlebearer, didn't he...?
Besides, even without population pressure, homosexuality is a wonderful form of birth control. It should be encouraged, since such a harmless lifestyle choice as homosexuality is far better than having our descendants killed off by starvation and disease from overcrowding, or having to live with forced sterilization -_-'...
Now, to just to convince people to not marry or have kids until they're 30...