The problem with these central banks is that they have kept price inflation too low for the investment markets to clear and money has been accumulating idle ins

The problem with these central banks is that they have kept price inflation too low for the investment markets to clear and money has been accumulating idle instead of being invested. Because they were late in their money printing, velocity dropped and they had to print much more getting much less effect per unit and yes did put the world at risk of future spike of inflation if this money starts moving. Sufficient high, well controlled, early enough inflation prevents velocity from dropping, prevents the investment and labor markets from jamming, prevents from having to print too much, prevents large stockpiles of idle money from accumulating and prevents later difficult to control spikes in inflation.