"When good does evil to fight evil, it becomes -- in T.S. Eliot's words -- indistinguishable from the evil it is fighting. War blurs the lines between good and evil so they are hard to recognize and traps those who launch them in Big Muddies of self-destruction."or as Bono wrote in 2000:
"And you become a monster, so the monster will not break you"....
and continues "but it's already gone too far, who says that if you go in hard, you won't get hurt? Jesus can you take the time, to throw a drowning man a line, Peace on Earth"
Despite rhyming "hurt" with "Earth", it's still a monster couplet from an album, "All That You Can't Leave Behind", that still resonates. (link is to a far left article, but the quote was interesting to me)
Update: "he who fights monsters should look to it that he himself does not become a monster. When staring deep into the abyss,the abyss stares deep into you" Friedrich Nietszche