To start with, it is imperative that the ECB sticks to its mandate to maintain price stability over the medium term. This, despite the many calls to widen its mandate to explicitly include financial stability considerations and/or domestic employment goals.
In theory, delegation of a task to an independent authority is more acceptable –  when the delegated task is clearly specified and has no overlap with other policy tasks;  –  when there are relatively few distributional implications;  –  and when a clear-cut measure of accountability can be achieved.