There are no degrees of "evil". Evil is evil, plain and simple, and deplorable in all cases. You don't compare evil acts to see which one is "more evil" than the other - hey, have you noticed that the term "eviller" does not exist?

So, the US prosecutes its evil-doers. Good, I would expect no less from a civilised country. The other side does not - sad and deplorable. But the fact that they do not (prosecute their evil-doers), does not justify evil in return.

So let's not try to justify lesser evils by the existence of worse ones. Yes, I know some live by demanding an "eye for an eye", but the majority have moved beyond that. And our own civilised status puts the onus on us to behave civilly even when the other side does not. Punish, yes. Commit evil, no.