I'm getting the sense that you haven't really read krugman. For starters, if you did read him on the NYT then you couldn't have missed the giant OPINION label at the top. It's an op-ed, it isn't claiming to be anything else.

Second, if you read the article in question he specifically talks about this particular school of economists using rigorous mathematical models, and the problems he has with those models (in laymans terms). Did you miss that part or did you not read the article in question?