The people who think that the trillion dollar is a "joke" are not drawing that conclusion as economists.  The Federal Reserve plans to add a trillion to its balance sheet in 2013 anyway and the difference between that, which is obviously not a "joke" since it is official Federal Reserve policy, and adding the trillion by means of seigniorage is essentially just technical.  If you have being following Krugman it would have been stunning if Krugman did NOT endorse it.  Krugman was already said the move is analogous to having the Treasury Secretary wearing a clown suit, and that could be pointed out, but if Krugman considers this a "joke" then he considers his own general prescription for monetary policy a joke.  If you think there's a danger in making too much out of this then the solution is to find one of the several instances where he distinguishes himself from the MMTers and add that as a qualifier.