That’s the classical argument and the one I’ve previously made, but the problem is the government just can’t do it anymore because the cultural forces that once took marriage seriously are gone from much of the First World. It’s not government that has been the driving force, it’s the culture. Government is just a reflection of what culture is, especially in a democratic government.
The SSM issue isn’t something that happens overnight----this is the product of a decades long decay of the institution of marriage that has been ridiculed and assaulted even in sectors of the religious community. In fact, when the debate was raging in America, people joked why GBLT would want to suffer through such a thing.
The government simply cannot be trusted, and if they get out of the marriage business altogether, the SSM movement loses a lot of wind of their sails.