Then again, you probably don't.
Again:
A necessary evil is an unfavorable thing 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 would be worse... In Common Sense, Thomas Paine described government as at best a “necessary evil.”...
The use of the term “evil” in the phrase does not indicate that the thing being characterized as a “necessary evil” is something that is generally considered an “evil” in the sense of being immoral or the enemy of the good. In Fuller’s use of the phrase, for example, there is no implication that court jesters are evil people, or having one serves an evil end.
Then again, you probably don't.