Deflation is a major threat for our economies. Though inflation has been falling for a long time, until now there has been almost no concern about deflation. This lack of regard is probably due to the macroeconomic theories that the mainstream has embraced. Money is not properly understood, and the role of banks in creating and destroying the money supply neither. Money is not only used for transactions, but also for saving. Irving Fisher in his book 100% money explains why banks contract the money supply in a depression. If he is right than Milton Friedman, who blamed the central bank for letting monetary supply, is wrong. Here is Fisher (p.78):

And the banks cannot help it. The public is quite wrong when, in the depression, they blame the individual bankers. It is the banking system – the 10% system – which is at fault. Under this system, the bankers cannot help destroying money when it should be created, namely in a depression; while in a boom they create money when it should be destroyed.