Human sexuality does not revolve around reproduction only. If it did, then sex wouldn't occur outside a woman's fertile period, and those fertile periods would be obvious to men. Such is the case among chimpanzees, whose females exhibit a far-from-subtle sexual swelling that peaks alongside their most fertile times. A close relation, the bonobo, has much more restricted female genital swelling, and humans have no detectable physical signs of fertility save slight temperature changes which would require sensitive thermometers to discern. As outward signs of fertility decreased, sex occurred more randomly, and evolved a social significance. Chimpanzees rarely have sex outside a female's fertile period, yet bonobos have sex frequently and without regard to a female's fertile period, and among all variations (male-male, male-female, female-female). Humans very clearly do not have sex solely for reproduction, and using the argument that reproduction is the only purpose for sex so as to denounce homosexual behavior is completely ignorant.
You've obviously missed the point, it isn't the only reason for sex, but that's what nature has designed for us to do. So yes having without reproduction is technically unnatural, but then again so is homosexuality. Like I said, I choose to have sex without having a baby, just like people choose to have homosexual relationships.
If homosexuality wasn't natural and normal for our species, it wouldn't have been occurring as frequently and for as long as it has, and we wouldn't even need to discuss it. Do we talk about whether or not it's natural to jab red-hot needles into our fingertips as a form of pleasure? No, because it's too uncommon to even be considered anything other than bizarre. Yet we continue to discuss whether or not an aspect of human behavior which has occurred for all known time across all cultures in about the same frequency is normal or not. Of course it's normal, within the context of observed behavior for our species. Frankly, if we weren't "meant" to do it, it wouldn't be possible. I personally don't believe in creation, so terms like "designed" and "meant for" don't mean anything to me, but you used it in your argument earlier. It's possible for me to stick my finger in my eye and blind myself. I don't think we were meant to do that. But then you say if we weren't meant to do it wouldn't be possible then go on to say you disagree with terms like designed and meant.. quite percuilar.