Nonsense. His most idiotic screeds are related to how the birth of George W. Bush has resulted in a massive depression. If there is a bit of economic sense left in that carcass, the fanatical, Bush hating, emotion driven part keeps it well under wraps. Check out his take on the current troubles. All Bush and lack or regulation. Moronic ranting of a seventh grader, not a first rate economist.
No, pay attention to his actual economic work, not his columns. As an economist he is first rate. His work on international trade, for which he won the award, is very influentially in the field of international economics.
His political columns are not the same level, but that is irrelevant.
You are going on his newspaper columns, which are idiotic enough. The Nobel Prize Committee evaluates what he has published in peer reviewed journals, which is very different. If you want to accuse Krugman of being schizophrenic, fine. Paul Krugman the populist columnist may be a nut case. Paul Krugman the professional economist is first rate, however.