No, it is a "beast" thing.. They argue they have urges and can't control them, and that is capitulating that you are not human, but nothing more than a beast of the field, and are not endowed with higher thought and reasoning.
Everyone has urges, however most people control the urges to do things they know are wrong... Homosexuals simply capitulate to them as any low level animal would.
I would argue that most mammals are actually quite "reasonable", and most birds, etc. I've seen it in action. They're not all just rote robots. They make decisions.
As far as reproduction, yes, they respond to urges. Yet unlike humans, they're only interested (especially the females) when "in season". Hence could it be argued that humans, unlike beasties, are constantly under the urge and more "beastly" by nature!
I don't think most people have the urge to "do" their own sex. There's no need to control an urge that isn't there. I firmly believe most homos are genetically defective, as are retarded people, etc, and cannot help being attracted to their own side. That doesn't mean, as with us normal people, they can't make the choice NOT to engage in sex at all.
Also doesn't mean there aren't homos who somehow, insanely made the choice to bed their own, perhaps ruined by some natural homo predator. Which proves my point. Noone in their *right mind* would choose their own sex for sex.