Negative interest rates are not absurd, Emil. They are a good policy step to solve the problem you describe.

The problem is an excessive unwillingness to lend without good collateral. That may be rational for the individual risk-averse saver, but leads to an equilibrium with too little investment and growth.

Don't think of negative interest rates as interest rates. Think of them as a small positive rate of interest plus a tax on excessive liquidity. (That's why negative discount rates don't cause infinite asset prices.). The negative rates correctly penalize excessive hoarding of liquidity and drive investors to take more risk.

Of course, I would rather this was all explicit. Central banks should not be tax collectors. Negative rates have unfortunate distributional effects - all taxes do - and these would better be imposed transparently by the political process.