An argument I think advocates of marriage equality should stress

I've commented here and here on arguments that I wish advocates of marriage equality would stop using, but there's one that I don't think they use often enough. Since opponents of marriage equality tend to use religion as a reason, or at least a pretext, we need to emphasize that at least here in America, as opposed to Iran, our Constitutional rights include freedom from establishment of religion, so that we should decide the scope of secular marriage under secular principles rather than any particular church's interpretation of Scripture. This argument must be a strong one, since whenever I bring it up, the 'phobes immediately change the subject.

In this regard, The Washington Post characterizes the view of anti-marriage-equality pastors thus:

But Thomas and the 77 other Baptist ministers in the association do not see same-sex marriage as a civil rights matter. Rather, they say, it is a question of Scripture, of whether a country based on Judeo-Christian principles will honor what’s written in Romans or decide to make secular decisions about what’s right.

Apart from the seriously question-begging reference to "a country based on Judeo-Christian principles," I agree completely with this framing of the issue, and under the First Amendment, the answer should be clear.

Enlightened self-interest should lead the pastors to the same conclusion. Do they seriously want the government to be the final arbiter of the correct interpretation of "what's written in Romans" or any other part of the Bible? What would they do if the government granted itself that authority and then took a position directly contradictory to theirs?