I've heard that sentiment expressed several times now... It's a very complicated thing right off the bat because marriage is really the only thing where church and state are intimately connected. It certainly does seem simpler from a logistics and political standpoint to sever government from marriage.
However, the government is responsible for the right social and civic order of the people it governs. Marriage being the normal base for families, and families being the essential building block of all human societies EVER, the government has an obligation to promote and defend marriage inasmuch as it contributes to the proper ordering of the state. And what way does marriage contribute? Well, it (usually) produces children IN A STABLE ENVIRONMENT in which children can be raised to be virtuous men and women.
Furthermore, the sociological chaos that would come from taking away the far more reliable measure of government records against this or that church's records is scary to think about... It would not be unimaginable that we might become two societies after not that much more nonsense: one of monogamous relationships done in more conservative faith traditions, and another of polygynandrous relationships where just about everybody is married to everyone else, or was at one point, done in either liberal faith traditions or in some "pseudochurch" for non-religious people. But at that point the question is: why bother with it at all? It means nothing. The whole point is for the STABILITY: social (children), emotional (personal), and practical (day to day affairs).
What do you think?
Your dreams can't catch you when you fall, but they sure can get you back up again.