Actually, I think it's the hypothesis (advanced by "essentialist" advocates of homosexual political causes) that has to be proven.
(Some) gays insist that essentialism is a law of nature and go off looking for "essentially" gay chromosomes, which they haven't found yet. But not to worry, it's only a building-block of a juridicopolitical strategy of obtaining Supreme Court decrees in their favor, so it needn't be "true" or "untrue" in ontological terms, but only bought into by five sitting Justices.
Essentialism, IOW, is a game -- linking homosexuality to the precedential condition of skin color, and the mass of civil-rights decisions compiled by the Warren and Burger courts.
Essentialist gays, of course, are undercut by gay advocates of "queer theory" who insist that sexuality is fluid and mutable in one person. But of course Evan Wolfson won't be inviting the queer theorists to submit a brief, when it's time to argue The Big One before the Supreme Court.
Now, if you'd like to talk about aversion therapy, I have a dead-tree copy of Irving Bieber's longitudinal study published in the 60's, in which he estimated, to sum up, that about a quarter to a third of the homosexual men he interviewed were highly resistant to aversion therapy and "essentially" homosexual, or at least homosexual at a level he couldn't reach with the analytical and therapeutic tools he possessed.
Is that what you had in mind?
Keep in mind that a lot of homosexuals are "recruited" -- sexualized while virgin and convinced they're homosexual. Gays actually try to do that, to reach virginal young men, because they know the power of "getting there first". Do you endorse that sort of homosexuality, the sexuality of victimization?
Do you endorse, approve, smile upon, or otherwise recommend to others any sort of homosexuality, on libertarian grounds? How about other paraphilias?
Just for fun:
http://scifipedia.scifi.com/index.php/Tok%27ra
Tok'ra:
The Tok'ra are a fictional race on the TV series Stargate SG-1. Tok'ra, literally translated, means "against Ra". They are of the same race as the Goa'uld but are diametrically opposed to them philosophically. The Tok'ra have fought the Goa'uld for several thousand years through infiltration and sabotage. They became allies of the Tau'ri, who provided them with hosts, including Samantha Carter's father Jacob Carter, who became host to the Tok'ra Selmak.
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Tok'ra Customs
** *
The implantation of Tok'ra symbiotes differs from the goa'uld. The Tok'ra, prefer to enter the body through the mouth, avoiding scars and pain caused by burrowing through the back of the neck as the goa'uld do. The lack of a scar may allow a Tok'ra to be overlooked as human when examined by a human. The Tok'ra like the goa'uld have naquadah in their blood however, an can be identified by goa'uld, Jaffa or former hosts.
The Tok'ra's relationship with their host is a balanced one. When one of the two desires to speak, they typically bow their heads, and close their eyes to indicate the change. Tok'ra also have romantic relationships with each other as Jolinar did with Martouf/Lantash. It is a complex relationship of four. When one Tok'ra is mated to another, typically the host and symbiote are both in love with both the partner's host and the partner's symbiote.
===end snip===
If I didn't know any better, I'd say he was new at this... He's not, in case anybody is wondering. He's just not interested in the latest science...