Necessary evil

Evil that is believed must be done or accepted

A necessary evil is an evil that someone believes must be done or accepted because it is necessary to achieve a better outcome—especially because possible alternative courses of action or inaction are expected to be worse. It is the "lesser evil" in the lesser of two evils principle, which maintains that given two bad choices, the one that is least bad is the better choice.

This keyword could refer to multiple things. Here are some suggestions: