There is no moral equivalent of the metal rod. If you cite the Bible, then you are arguing a tautology: What the Bible says is right IS right, because the Bible is the word of God. How do we know it is the word of God? Because it says so in the Bible.
There are certainly biological arguments against homosexuality. But there are identical arguments against anal heterosexual sex, oral sex, and other practices.
Ultimately, moral arguments do not need to be bolstered by reason, nor do they need to withstand reason's test. In many cases, moral codes (norms) derive from social utility, and violation of them has negative consequences. But that model puts the cart before the horse: behavior creates morals, not vice versa.
In the purely moral model, one must admit to a transcendent authority who is the author of absolutes. Those absolutes may or may not withstand the scrutiny of our puny reason.
I like that:
"In the purely moral model, one must admit to a transcendent authority who is the author of absolutes. Those absolutes may or may not withstand the scrutiny of our puny reason."