Maybe they do, but using the idiom “necessary evil” doesn’t make it certain that they do. Probably nearly nothing colloquially described as a “necessary evil” is actually “evil”. It can be only a pain or an annoyance, but required.
>[…] the use of the term "evil" in the phrase does not necessarily 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.
Maybe they do, but using the idiom “necessary evil” doesn’t make it certain that they do. Probably nearly nothing colloquially described as a “necessary evil” is actually “evil”. It can be only a pain or an annoyance, but required.
>[…] the use of the term "evil" in the phrase does not necessarily 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.
— https://en.wikipedia.org/wiki/Necessary_evil