The only way bitcoins are being generated is by wasting computer cycles solving problems that are of no use to anyone. Krugman's problem is not with the concept of bitcoin, but the process of mining.
I may not be an economist, but the method used for mining seemed.. illogical to me as well. If a bitcoin was released into the wild based on running real world problems like folding@home or something else it would have much more sense to me.