If a valid argument against homosexuality existed, would you admit that it did?
It's just that the OP seems like a trick-question.
Yes.
I'll admit that maybe I'm the one person who misread the OP but taking the phrase an argument
against homosexuality is to make an argument against what we know homosexuality is. Not gay sex. Not just love between members of the same sex. The whole concept. And the against part is to show that homosexuality is not a choice. That was implied by removing the religious aspect of it because the primary religious argument is that homosexuality is not biologically determined.
That's why I kept repeating back to arthra's posts because he attempted to put forth the non-religious, psychological argument that homosexuality is a natural but detrimental state of being. An argument that homosexuals could indeed choose to not be that way, which implies the same for heterosexuals, would be an argument against homosexuality. For it would be an argument stating that human sexuality is merely a choice.
In other words, an argument against what we know what it is today.
Past arthra's arguments all we've seen are arguments as to which state of sexuality is better. From my understanding of the OP that is not the question.
I'll change my opinion in a heartbeat when the empirical data suggests that my currently held opinion is wrong on any subject.
I don't think the OP is a trick question. It's just that outside the realm of faith, whether one believes homosexuality is biologically determined or not, there are no good arguments against the existence of homosexuality as we understand today which is that it is a biologically determined state of being.
I would expand to include all of human sexuality and human sexual development.
Now if the OP meant arguments against homosexuality in the sense of whether or not society should accept homosexual relationships than I think we are all off track in the debate. But I don't think that was the intention since religious based arguments were specifically exempted and highlighted by the examples in the OP referencing design or natural state of existence.