The part in bold is false. Biologism is not a factor in constitutional debates. It is not relevant to the debate at all -- as you point out, it is only of interest to people who are predisposed to consider homosexuality wrong or immoral or potentially illegal. They are looking for evidence that it is not biological.* That may/may not mean there is "less basis" in terms of meandering public support, but not at all that it has "less basis" in the constitution. The constitution protects all kinds of individual rights and freedoms that have nothing at all to do with whether those freedoms are genetically inherited or can be justified as "biological". I doubt there are ANY (right, left, center) judges or politicians that will want to make "scientific biologism" of this sort an element of the constitution -- you might as well throw the whole thing away.
my comments are very much related to the battle of banning gay marriage and whether that it constitutional in the U.S. I just wanted to make that clear for anybody reading this.
I'm saying that if homosexuality is not a choice, then there should be no debate about whether gay marriage is allowed, as it would clearly be discrimination against a class of people to not allow them to marry.
If homosexuality is a choice, then you get into a much murkier area about what is allowed and what isn't according to our Constitution. There would be less basis for overturning laws voted on and passed by the people of individual states. I would still feel it should be allowed (no question), but I don't know if laws banning it should be overturned.
However, I think the idea that homosexuality is not biological is only controversial amongst gay marriage opponents. The science backs it up, and it doesn't make sense any other way, which means that there isn't much doubt in my mind.