If I were up to it, I would try to defend the constructionist thesis but I'm lazy. So I would just say one, if we were holding an essentialist position* we would have to explain the reasons for which the historical and anthropological actually seems to contradict this. Of course an ethnography or historical report can never be scientific in the way, say, a population-quantitative analysis can be (Is that bad?) but it's also clear that historians and anthropologists are not creating things out of thin air. Well, except the most demented of Foucault admirers.
(* - As I mentioned earlier, a lot of the claims for the innatist position are based on twin studies. But even the highest twin studies afaik record that in cases of identical twins if one is gay there is only a 52% chance that the other one is. Given that identical twins are supposed to be identical genetically, if homosexuality was purely genetic than that number should be 100%. This suggests that biology of it is more complex than most are willing to admit. There's also a problem of trying to explain how homosexuality could exist under standard evolutionary theory which suggests that such a trait - that isn't passed on to offspring - could exist. There's a lot of "It stands for reason" going on here on both sides. And reason, like common sense, is the collection of prejudices we all get by the age of 18)
Angela and Maria Eagle, identical twins and English politicians - both are Labour MPs for constituencies in Merseyside, both are keen chess players... yet one is a lesbian and the other is straight
Ftr, my position on this is "who cares, really?" But I will admit that I find the notion of sexual identity highly dubious.
You're right on the money here. From the limited stuff I've read, it seems like the cause of Homosexuality is as much pre-natal as it is genetic.
