It matters whether the investment is good or bad

Regarding Paul Krugman's editorial "Bits and Barbarism" I'll leave it others to comment on Gold and Bit-coins and dwell on the Keynesian idea that it doesn't matter how the money is spent for the economy to grow. While World War Two did pull us out of the depression and war is pure consumption, this economic notion of Keynes needs testing in other settings. The recent global mal-investment in real estate is a drag that would not be reversed by additional spending in housing. Japan's inability to pull out of it's lost decades comes in spite of huge infrastructure expenditures tried in the 90's. Nor should we expect the forthcoming clean up spend on nuclear waste and plant dismantling will help out, especially if every nuclear facility lays dormant as another of the country's mal-investments.