From another reader:
Your correspondent is being silly. Brooks isn’t saying that lefties would be morally superior had their opponents beaten them on an anti-gay-marriage agenda. He’s saying that they would FEEL morally superior, by their own definitions of “moral” and “superior”. When your moral code elevates gratification of self over the integrity of the institution of marriage, and an absolutist conception of “choice” over the right to life of unborn children, you can feel “morally superior” without being so. And someone else can acknowledge your conceit without validating it.