The argument against gay marriage depends on the contention that gay marriages are fundamentally different than conjugal marriages. But the titanic hole in that argument is that gay marriages are exactly like conjugal marriages that don't produce children. Slightly over half of all conjugal marriages don't produce children, and we don't ban conjugal marriages that can't produce children, or prevent opposite sex couples who say they don't want chldren from marrying. So what's the compelling state interest in not allowing gay couples to marry?
Right, there is none. There needs to be a more compelling state interest beyond "some of the people in American don't like this" in order to continue preventing gay couples from marrying.