State-sanctioned marriage is a civil contract, period. A contract is not a judgment of moral value. It is a legal agreement between two parties that testifies to a meeting of minds between those consenting entities. It is not a religious act or rite and so has nothing to do with Adam and Eve or Steve or even Harvey.
Yet, history has shown that if material force can defeat some ideologies it can no longer obliterate a civilization without destabilizing the whole planet.