It doesn't really matter if Nakamoto really is the NSA (maybe "Satoshi" is the middle name and his first name is even Aaron, making the initials NSA, did anyone ever think of that?!), the protocol is open and any weaknesses or backdoors would eventually be discovered.
Krugman was a proponent of mass inflation, aka. helicopters of money, as a solution to the credit crisis. Bitcoin makes it basically impossible to manipulate the money supply the way the Fed has done to navigate the 2008 crisis.
Krugman sees Bitcoin as a threat to the central banks ability to stabilize the economy.
https://twitter.com/rabois/status/426157931239714816