The usual argument for why negative interest rates might be needed is to prevent deflation. But in a fiat currency system like we have, it is always extremely

The usual argument for why negative interest rates might be needed is to prevent deflation. But in a fiat currency system like we have, it is always extremely easy for governments to reduce the value of the currency (ie, stop deflation). They can just print more money. In detail, they can just finance government expenditures with money created out of nothing, if necessary cutting taxes to provide more need for money to be created that way. This is in fact what has happened many, many times. It's not some strange fringe theory. There is no doubt whatever that it works. There is no need for negative nominal interest rates.