Why is the ECB keeping interest rates zero or negative?

Why is the ECB persisting with zero or negative interest rates despite the drawbacks of this policy (weakening of banks, life support for “zombie” firms, inability to lower interest rates if necessary, excessive taxation of savers)? We see three possible explanations: The ECB still believes that doing so will eventually lift core inflation (which seems increasingly doubtful); The ECB wants to boost countries’ solvency (but they would still be solvent with interest rates at an intermediate level above zero); The ECB wants to combat the excess savings in the euro zone (but fiscal policy would be a more effective instrument). Our concern is that the zero interest rates will end up achieving none of the ECB’s objectives, while the associated drawbacks will become ever more severe .