Firstly, note that these are negative <i>deposit</i> rates. As a bank you have to keep your spare money somewhere, and that is usually in an account at the local central bank which also serves as part of the interbank clearing system. Central banks are now proposing charging for keeping excessive reserves in this account.<p>The bigger picture is that wealth accumulation <i>cannot</i> outstrip economic growth long-term or even medium-term without causing serious strain somewhere. Pushing the rate of return on capital negative is the gentlest possible way to do this. But the real problem is real estate and its endless appreciation in value.