If one knows there history, marriage was created by God. The act of joining people through a "holy matrimony" was ordained through God's word and carried out by the church. So... if a gay couple believes in God, why would they want to go against their God's word. (this would be like passing a law that allows theft) If a gay couple does not believe in God, why would they want to take part in a sacred (holy) union created by one they do not believe in. (with civil union, there are no additional benefits, unless the benefit is the rewards of acting like believers, or going against God and believing they win)