The implication that I believe you are missing is that all humans are to some degree evil, and that goes doubly so for the type of human that finds themselves working in the world of politics.

It's tongue-in-cheek, and that was very well known when the phrase originally came out.

The subtlety seems to have been lost over time.

Someone read that quote from The Witcher, not recognizing it was planted right at the beginning of a character arc of growth.

That phrase is aggressively fucking stupid.

Nothing is pure and virtue doesn't matter. And even if virtue did matter, when you decide not to choose you are just as culpable with the result when it is the worse evil.

You can't wash your hands if you had the power to act.