The doing an evil to avoid an evil cannot be good.

Harm done to prevent harm is still harm, and calling it necessary does not change what it is. The reasoning that permits it is always available, and once that logic is accepted almost anything can be justified by naming something larger. Sometimes a genuinely bad option is the least bad one and has to be taken. Even then it should be carried as a cost, not converted into a virtue.

If you are about to do something you would condemn in someone else, say the reason out loud in plain words. Then decide. Whatever you choose, do not tell yourself it was good.