That is the central question, and the true reason all freedom-loving citizens -- Christian or not -- should oppose faux marriage. Should we allow the government to force us to recognize certain institutions as morally acceptable when our own beliefs, passed down through ages of history and civilization, insist they are not?
Does the government exist to define morality, or does it exist to enforce the morality defined by the people? In the case of homosexuality, it is the former, and a gross abuse of power.
The most concise and brilliant statement I've ever read on the topic.
For the amoral liberal, the government exists to define morality and take the place of God. It is that simple.