Ramesh, I think the answer can be found in, so to speak, the ellipses. Here’s the full paragraph:
“Conservative atheists and agnostics support traditional American values. They believe in personal responsibility, self-reliance, and deferred gratification as the bedrock virtues of a prosperous society. They view marriage between a man and a woman as the surest way to raise stable, law-abiding children. They deplore the encroachments of the welfare state on matters best left to private effort.”
I think that she’s using opposition to same-sex marriage as an example of one traditional American value (among many) that atheist and agnostic conservatives can support, and I suppose she’s right, although whether opposition to such marriages is automatically part and parcel of being conservative is an entirely different question.