I know a gay guy from a philosophers cafe I used to attend in high school. We're still friends, and we've talked about this topic a few times, so I'll give what opinions I can recall.
As to the nature of being gay, he told me that at first he wanted a girlfriend because he knew he should want one, and because he thought girls were pretty. Eventually, over the course of his high school years he realized he was more physically attracted to other guys, and he decided to be open about it. The key point is that he told me he never wanted to be gay, nobody he knew wanted him to be gay, and the few girls he did date gave him nothing but good impressions of the female sex, and in fact he has way more female friends than I do, at this point. He really didn't see anything that would have made him have those feelings, and I'm inclined to agree.
Anyways, since having kids is socially acceptable, and since humans are by nature social creatures, it follows that even gay people will have sex in order to procreate. In addition to this, it is known that gay is not a single trait, nor can it yet be determined by genes whether or not someone is a homosexual. It's a brain thing, and as such, very difficult to attribute to something that would get ironed out by evolution. Even in primitive societies, a man who did not have sex with women was almost unheard of, and it is easy to understand why they would have sex with a woman to make children. So, even if it is a removable trait, there's no reason that it would have been removed.
In terms of philosophy, we should step away from an evolutionary standpoint and look at things differently. Most of the sex heterosexuals have is hedonistic in nature, in fact, most of us don't have kids, so 100% of the sex we have is hedonistic in nature until we do so. The statistic is that the average human has sex about 4500 times in their life, but that the average north american parent has 2.3 kids, that's something like 99.95%. By that regard, saying that gays should not have the ability to engage in hedonistic sex is laughable at best, considering that if we have heterosexual sex for enjoyment, they should have what they enjoy the most, just as often and with as much impunity as we do. Humankind has developed past the point of animal tendencies, yet sex remains, for all of us, as a necessity in order to be satisfied with life (in most cases, by psychology) As such, since we want sex without children in order to keep ourselves satisfied, there is no reason to say that some minorities should be excluded from that. The only passable argumens I've heard against homosexuality are religious in nature, and are invalid unless the princibles of an ancient book and the misinterpretations of countless religious people are held to be undeniably true premises.
None.