It's even worse than that, the anti-God libertarians have started using a holier than thou tone, to convince Christians that the true moral position is to quit fighting for conservative politics, and to drop out of politics, and leave that part of life to everyone else.
I think the point is that by taking marriage away from government, you will not have to fight it out to protect marriage in the first place. In order to protect it by fighting it out in the arena of politics, you will need to win every election, you cannot afford to lose one. One Democrat President, One Democrat Congress, you lose. Why give your enemies the stick to beat you over the head with. I would prefer to take that stick out of their hands.