“The sexual union of a man and woman is called the marital act because the two become physically one in a way that is impossible between two men or two women.”
Many make the mistake of thinking that opposition to gay marriage is religious. A Facebook friend recently posted this quote: “Have you ever noticed the same people who claim that marriage is a religious institution only think that LGBT people shouldn’t get married? They never seem to object to Hindus, Muslims, Buddhists, or atheists getting married.”
This is a perfect summary of the ignorance with which many (though by no means all) gay marriage proponents operate. And I think their ignorance is largely the fault of religious supporters of traditional marriage who have forgotten the categories of reason and nature.