Negative rates are effectively a tax on deposits, and as such are intrinsically contractionary. They are a form of financial repression. As long as banks choose to absorb that tax themselves, those who pay that tax will effectively be bank shareholders and employees. But if banks choose to pass that tax on, it will be savers and borrowers who pay the tax. Would the increased economic activity that negative interest rates may generate be sufficient to offset the effect of this tax?
Alternatively, if we think of negative rates as a monetary operation rather than a tax, we can say that the central bank drains back a small proportion of the reserves it adds to the system through QE. This is monetary tightening. Again, would the increased economic activity generated by negative rates be sufficient to offset this effect?