Krugman Unintentionally "Refuting" Leftist Theory On Crime
But if we are to use such crude empiricism to refute conservative beliefs about the importance of marriage, then we can use it against leftist beliefs too. Because this drop in crime has also happened during a period when, as Krugman and others insist again and again including in this post, inequality has increased. This means that by Krugman's logic he is refuting the leftist belief that inequality and poverty causes crime.
Now, I would say that the drop in crime is a result (mostly, there are probably other factors as well) of tougher sentences and better police methods and that it doesn't prove much about the effects of either marriage or inequality, except perhaps that their effects aren't that great, but the point is that if an aggregate change in crime is accepted as evidence of the effects of marriage then it can be accepted as evidence of the effects of inequality as well.