There is little doubt that science will ultimately give us the cure for homosexuality. In my mind, homosexuality has nothing to do with morality, hence whatever its cause it changes nothing about its moral status. If it is a defect arising in fetal development it certainly cannot have a moral component, just as any other fetal defect.

You say that homosexuality has nothing to do with morality, but your acceptance of the idea that homosexuality is a "defect" demonstrates that you have made a moral judgment about homosexuality. A true birth defect is something that causes harm to an infant or that diminishes an infant's ability to engage in the activities that we consider a normal part of life -- like the ability to see, speak, or walk. Being gay does not diminish a person's ability to engage in the activities that are part of life. Gay and straight people are both equally able and equally likely to have happy, fulfilling sexual, romantic, and family lives.

Being gay is a difference -- it is no more a defect than being blond, blue-eyed or left-handed.

JonboyDC:

Being gay is a difference -- it is no more a defect than being blond, blue-eyed or left-handed.

Being born blond doesn't affect behaviour all that much, blond jokes aside. There is obviously some evolutionary reason for a signifigant percentage of gay people persisting. Perhaps we're just stuck with a system that mostly works. Or maybe there is/was an advantage in the conditions that cause risk. Or maybe there is/was an advantage in non-reproducing relatives. I think it's fair to say it is either defect or design, as being gay does affect reproduction, though that is changing.

Sexual orientation does not affect ability to reproduce. You claim that it does, then suggest that that is changing. In fact sexual orientation affected reproduction much less before the 20th Century than it has in recent decades. The decline in procreation by same-sex-attraced individuals is recent and due to the construction of the "gay" identity and culture. Before the late 1800s, same-sex-attraced individuals almost always married and made babies in the usual way. Now people are choosing to make babies in other ways, from withing the gay community.

The culture war is in fact the only war. As left-handedness lost its moral - cultural - meaning as, it came to be seen as a trivial difference, not as something sinister. Would anyone take seriously the claim that left-handedness is a defect, disease or deficit - something that should be cured, corrected or suppressed? If someone were to make such a claim, seriously, how would we view him? As a kook? As a bigot? Worse? When people abort their female fetuses, as if being female is a defect, deficit or disease, what kind of moral - cultural - judgement should we/do we make of them? Only a cultural shift will drain gender and sexuality of their cultural values so that they can be seen for what they are: like handedness, mere differences among people that make the world a richer place.

Go back a little further. I was not arguing ability, but likelihood. With a social stigma, you have pressure to pretend to be straight. Go back far enough, and this is very unlikely to be the case. But we can also look at animal behaviour (ie rams) where we know it affects reproduction. The question is, why does it persist?