Gay marriage has been put to a vote in 32 states. It is currently 0-32.
Of course, while it fails democratically, it also triumphs legally. Being on the anti-democratic winning side helps make it the central issue of contemporary liberalism.
I stumbled upon this comment somewhere, but have lost track of who said it:
"To be against gay marriage, at least in the views of most liberals ..., is to disqualify oneself from society as a hateful bigot."
I think that exemplifies the main driving force of modern liberalism. It's not intellectual. In spirit, it's more like the caste system in India. It's a system for identifying new Untouchables whose very existence lifts the social status of the liberal. India is a pretty crummy place, but Indians like it because hundreds of millions of Hindus have hundreds of millions of lower caste Hindus to look down upon. So, they've got that going for them.
Gay marriage, for instance, is a trivial issue in real world terms, but it has become incredibly important to liberals precisely because it brands huge numbers of their fellow citizens as Dalits for them to hate and feel morally superior to.