This discussion has just gotten too unfocused.
So let's look at what we're actually worried about which is the right-religious argument against homosexuality. To believe that argument you must believe THREE propositions
1. There are only two natural genders.
2. Men and women are naturally heterosexual.
3. Nature is designed by a moral intelligence.
If and only if all three propositions are true, then homosexuality is immoral.
So is the first proposition true? Sexual dimorphism in higher vertebrates has been stable and self-perpetuation for millions of years. So the evidence clearly supports that proposition.
Is the second proposition true? Well, the historical evidence and evidence from the behavior of our primate relatives says it is true of a majority of individuals but there is also consistent evidence of homosexual behavior over thousands of years. Also, this incidence of homosexual behavior seems relatively stable and self-perpetuating despite an obvious possibility that it could affect reproduction rates.
Of course the third proposition is totally discredited, disproved time and time again and has no predictive or analytic value.
Even if the first two propositions were perfectly true instead of being conditionally true, the falsity of the third destroys the argument. Therefore - and this is essential – any suggestion that homosexuality is immoral because it is "unnatural" is necessarily false. Nature does not reflect a moral design, thus even a valid claim that something was "unnatural" could not be a moral argument.
I know of no other moral/ethical test which consensual homosexual conduct fails, and neither does our conservative Supreme Court. So it seems to me that time taken worrying about a morality argument against homosexuality is time wasted. Ethically, it doesn't matter why people are gay. It has no moral consequence.
As to the political arguments about homosexuality, it seems to me there is a clear, libertarian limit to any discussion. Even if we accepted the Scalia view that regulating homosexual conduct is within the rights of the state, why regulate it? If there is no moral/ethical reason for people not to engage in consensual, homosexual activity, what interest does the state have in doing so? Sex between adults and children or animals fail both the consent and the cruelty tests. I don't know of any moral test that polygamy fails convincingly, although I am suspicious of it in feminist terms. In some sense divorce has allowed a sort of polygamy back into our culture, so maybe it's not a big deal. The libertarian acceptance of homosexuality is more important.
So what of the other propositions put forward here?
Let's take a few:
1. There are more than two genders.
2. Human sexuality is primarily a product of socialization.
3. Heterosexuality is not instinctive.
As to the first proposition I cannot state it in terms of a number of genders larger than two because no number has been agreed upon and no consistent definition has been put forward. The closest definition has been that gender is what a person is recognized to be by other people. The problems with that are that most people only have two gender categories they identify a person as belonging to and recognizing a gender is subjective. Moreover, the idea of categorization itself has been brought into question on this list.
The second proposition runs into the major problem that sexual desire consistently develops with physical sexual maturity, also the fact that sexual desire can be manipulated chemically. So the underlying desire to have sex certainly seems a product of biology. In addition, sexuality clearly predates language. As language developed, at no time could incomplete language development have stopped our ancestors from being sexual and reproducing. Possibly humans are now so dependent on language that without it they would not be sexual but I don't know of any evidence that this is the case, while there is consistent anecdotal evidence of humans' having sexual relationships without speaking each others' language.
What we find sexually attractive and why is just too complex for me to speculate on. I don't have any basis to argue that it is or is not social.
The third proposition runs into the problem that heterosexual behavior predominates in our own species and in all our closest relatives. To the extent we are a product of biology, we are a mostly heterosexual product. Heterosexuality also predates language so it really cannot be a social construct.
What is also unquestionably true is that we are, by higher vertebrate standards, hyper-sexual and so are some of our close relatives. Female Homo sapiens are receptive to sex (that's the way the biologists talk about it) throughout their entire estrus cycle and all times of the year. All evidence suggests that this has always been so. Since biologists mostly characterize animal sexuality in terms of the sexual behavior of the female, that makes us a hyper-sexual higher vertebrate. There is evidence of consistent homosexual behavior in our species and our close relatives, but this is not often totally exclusive of heterosexual behavior. Many individuals that engage in consistent homosexual behavior have had children, nonetheless. Because we are hyper-sexual most of our sexual activity is not procreative anyway. A biologist looking at our species from afar would probably characterize us as hyper-sexual before homosexual, since that is the clear distinction from other higher vertebrates and biologists look at sex mostly in terms of reproduction.
Peace
boddi