
Remember, Sweden is the place where, if you use too much cash, banks call the police because they think you might be a terrorist or a criminal. Swedish banks have started removing cash ATM machines from rural areas, annoying old people and farmers.
If banks charge customers negative rates of interest in a cashless society, those customers are not able to withdraw their money as cash to shield it, under their putative mattresses. Consumers’ only choice in such a scenario is to spend it or let the bank take it. (The theory is that by forcing people to spend cash rather than save it, you can spur economic growth.)