Far as I know, there's no NEED for interacial marriage, nor is there any reason to ban it. I mentioned infertile couples b/c most people try to argue that if the prohibition on gay marriage is due to inability to reproduce, then shouldn't infertile heteros also be denied.
Using your reasoning, perhaps we should allow public masturbation and coitus so long as the people involved clean themselves up and not contaminate anyone/thing.
Actually, I believe you (or someone else) was corrected about that in an earlier post. Such marriages weren't sanctioned, but homosexual activity wasn't necessarily discouraged.