A reader writes:

Jonah,
I don’t know if you are going to bother to respond to Yglesias’s response to your response, but it would be a shame if you just let that last paragraph of his response hang out there. It is really outrageous.
Yglesias is surely right — moral argument is not like mathematics. You can’t prove you are right and the other guy is wrong if there is no shared set of principles or axioms or even sentiments to which you can appeal. If that’s all he means when he says he’s a “quasi-realist” then that’s fine. He has made a merely descriptive point about the power of moral reasoning, and one that is obvious. People agree to disagree all the time, and there is nothing you can do about it.
But notice the extraordinary leap he takes from this noncontroversial proposition. Because you can’t persuade Hitler and his followers that they are wrong, we must conclude that they are no more “wrong” than we. The impossibility of persuasion makes the concept of “right” and “wrong” useless, in his view. And when it is useless, then it is just fine to use force.
But if the measure of the validity of moral argument is its utility (I’m conceding that for purposes of the argument — I don’t believe it) then why is persuasion of your interlocutor the only way moral argument can prove useful. Yglesias’s moral view accepts the necessity of war, at least against Hitler. Ask yourself: would the soldiers have gone off to war, and would they have been as effective, if our moral discourse about that war amounted to the Yglesias view? “We have tried to discourse with Hitler, but we have determined that his fundamental way of thinking is not ours. As a result, we have no way to determine who is right and who is wrong. So your country asks you to give up your lives for our fundamental way of thinking, even though we have no idea if it is right.”
This is no way to run a third-rate nation, much less the most powerful nation in human history, which has done more than any other to spread the principles of liberty and equality that enable Yglesias to grouse about relativism.

Me: I’m not getting back into this, really, but Yglesias’ view does call to mind Richard Rorty’s observation about the consequences of such views: “This means that when the secret police come, when the torturers violate the innocent, there is nothing to be said to them of the form ‘There is something within you which you are betraying. Though you embody the practices of a totalitarian society which will endure forever, there is something beyond those practices which condemns you.’”