What they don't seem to understand is that negative interest rates mean the death of currency.
We are already in a zero-rate environment. When you adjust for taxes and a couple of percent inflation, any “safe” instrument you can buy yields a negative return. This would just make it “official.” And, it would more than likely only apply to deposit/demand accounts.
I agree that a negative real rate (after inflation and taxes) robs savers, but we have it already.