I've been thinking about the issue Radley raises about the same-sex marriages in San Francisco as well. And I think he's put his finger (or Insta's I guess) on the puzzle for me too: is it a legitimate form of civil disobedience for an agent of the state to violate a law he or she has sworn to uphold when he or she believes that law to be immoral? My own view is that the constitutional principle at stake trumps the importance of the "rule of law" in such cases. If the Mayor of SF genuinely believes that the current law that prohibts same-sex marriages is unconstitutional, then I see nothing wrong with him attempting to violate that law, peacefully, to make a point. Radley's race analogy is very telling.
But here's another fly in the ointment: As Rod Dreher points out in The Corner, what precisely is the difference between this situation and Judge Moore's refusal to remove the Ten Commandments from his courtroom? Surely Judge Moore perceived himself in exactly the same situation as the mayor: caught between obeying the law as written or obeying a more abstract moral/constitutional principle. My own view of the constitution leads me to believe that the mayor is right and Moore is wrong, but that judgment rests on my reading of equal protection and separation of church and state. In some objective sense, I'm not sure there is a difference between the two cases.