Krugman is fighting an old war.
Our current economy is not encumbered by too little demand - but by too much supply from past capital misallocation.
Our addiction to QE has made problem far worse. Asset markets are exploding in price higher due to central bank intervention while incomes are not.
http://www.reuters.com/article/2014/10/31/us-japan-economy-b...
The European Central Bank announced QE in Jan-15.
One way to think of QE is global competitive devaluation to capture global demand. QE + ZIRP or even negative interests are the primary tool of central banks now. Capital misallocation continues on a global scale.
http://www.vox.com/2015/2/5/7981461/negative-interest-rates-...
e.g. Cash is not secure in your bank account. A government backed bond, even at negative interest, may be more secure than a cash balance.
ZIRP and negative interest rates are pushing people out on the risk curve and raising asset prices.
As I said in an earlier comment, IMHO, all investment decisions are bets on central banks.