Well thats what happens when the government gets involved and contractualizes it with certificates. If christians want the religious benefits of marriages do them through the church. If any two adults want the legal benefits of marriage go through the government. Yet even most christians would be opposed to gays getting the same benefits through the government.
A contract would be one thing if we respected the nature of law or at least tried to, but you are hard-pressed to find someone who does. Laws are no longer reflective of immutable principles, but rather flippant edicts that serve as political or personal weapons. Which is to say, Law no longer exist in the truest sense of the word.
Where does that leave us? Bickering over who gets what benefits. Over who has what powers when someone warms the seat of an elected office. Over definitions as God would have them and as Man would have them. Like crows picking at the corpse of a thoroughbred.
It's a long way home, America.