I was listening to Tell Me More yesterday and was drawn into the story.
The host interviewed Michael Crawford, a DC-based activist. He attempted to debunk the idea that black communities are strongly anti-gay marriage. They played a clip of former DC mayor Marion Barry explaining how he personally might approve of gay marriage but he felt he had to represent his constituents by voting against it. Crawford called him out on a couple of scores. First, Crawford pointed out that Barry gave no polling data. Then he pointed out that he has the support of a large coalition of clergy, contradicting Barry's claim that clergy don't support gay marriage. His most important point, though was this:
Traditionally we have not put the rights of a minority up for a public vote.
Really, there's no better argument. It leaves those who oppose marriage equality with nowhere else to go rhetorically. They are either bigots who want the law to support their own biases, or they are bigots who want cover from other bigots on a ballot.