I like this and agree that usually or at least often the people making these "I don't understand how anyone could ..." statements aren't interested in actually understanding the people they disagree with. But I also liked Ozy's comment:

I dunno. I feel like "I don't understand how anyone could believe X" is a much, much better position to take on issues than "I know exactly why my opponents disagree with me! It is because they are stupid and evil!" The former at least opens the possibility that your opponents believe things for good reasons that you don't understand -- which is often true!

In general, I believe it is a good thing to admit ignorance when one is actually ignorant, and I am willing to put up with a certain number of dumbass signalling games if it furthers this goal.