EFS,
Yes, I figured that one out. I'm suprised I forgot about your post to the marriage thread... but it was a while ago. And you never did answer my follow-up question.
As for pair-bonding... are you saying that love (romantic love, the kind you "fall" in) isn't instinctive? Or just that it doesn't promote pair-bonding? Either way, I beg to differ. Our instincts push us to fall in love, which leads quite naturally to long-term relationships. Our instincts may also push us to be non-monogamous within those relationships, because there's an evolutionary advantage to genetic diversity... but that doesn't override the basic pair-bonding instinct, it just supplements it.
But I'm getting off-track. Am I correct in assuming that you believe the "true purpose" of sexuality is reproduction? In that case, why do you think a couple may be sexually interested and active at any point in the woman's cycle of fertility -- rather than at its peak, which would be more efficient? I believe most animals function that way... dolphins and chimps are the exceptions I know of, off-hand.
If you have evidence to show that asexuality is a social anxiety disorder, that would certainly be relevant to the topic, although we seem to have drifted off almost entirely. I agree that asexuality is an apple to homosexuality's orange, or vice versa, if you prefer. And I don't know what you mean by "the drive to gratify" being a shared quality. since I think asexuality is, by definition, the lack of such a drive.
I believe humans have an instinctive aversion to incest... which is why people arguing against homosexuality like to trot the argument out. But because of that instinct, true incestuous relationships are inherently dysfunctional. Now, if you had two people who were closely related genetically, but did not have a pyschological history as, say, siblings... then I think they could have a normal relationship. They'd just have to be very careful about birth control. The thing is, the vast majority of cases of incest are not going to be Luke-Skywalker-meets-Princess-Leia coincidences, they're going to be between actual family members who are seriously messed up.
Now, you'll probably take this and say people are inherently heterosexual, so any homosexual relationship is equally dysfunctional... and I'll agree with you, up to a point. Most people are heterosexual, and heterosexuals should not be engaging in homosexual relationships. But there are a minority of people who have the "wrong" sexuality for their sex -- I've mentioned before that I think homosexuality is probably a subset of transsexuality -- and for whom heterosexual relationships would be just as wrong.