Paul Krugman is right if he is talking about a small attack by the bond vigilantes. It's a good thing, because it increases Aggregate Demand, which is what the US economy needs.
But too much of a good thing will be a bad thing.
A large attack by the bond vigilantes would be a bad thing, because it would increase Aggregate Demand too much. That would force the Fed to increase interest rates a lot, and that would force the US government to raise taxes and/or cut spending to cover the increased costs of servicing the debt.
If the bond vigilantes suspected that the US government could not or would not raise taxes and/or cut spending to cover the increased cost of servicing the debt, the bond vigilantes would all attack en masse.
If the debt were small, the amount by which taxes would need to be raised and/or spending cut to cover the increased debt service costs would be small too, and it could easily be done. But if the debt were large, the amount by which taxes would need to be raised and/or spending cut to cover the increased debt service costs would be large too, and it could not easily be done.
The longer the US stays in recession, with a large budget deficit, the bigger the debt will grow.
This does not look to me to be a very stable system. And the longer the bond vigilantes wait before attacking, the less stable it looks.
Japan looks even less stable than the US.
The bond vigilantes will eventually attack and rescue the US and Japanese economies from recession. But every year they wait before attacking, the bigger that attack will be. And they won't attack until they have grown bigger than we would want them to be.
To my mind, this reinforces the urgency for something like NGDP targeting. We don't want to wait for the bond vigilantes.