Is there such thing as justifiable vengeance?

Well, the one thing you can say about capital punishment is that that particular perp won't do that particular crime ever again. Doesn't make the world a better place, necessarily, but it certainly makes that one little corner of it a bit safer. The "turn the other cheek" "Vengeance is mine, mumbles the lord" kind of shinola is the kind of maundering one expects from perpetual victims. If you KNOW that the bad guy is guilty and the system is not taking action, then you would be justified (morally, not legally) in exacting vengeance. But (and it is a collossal caveat) certainty is hard to come by, and there will be repercussions from vengeance (either by the system or by the perp's confederates) that must be weighed. In the end, evil is frequently its own reward - violent criminals tend to die violently, whether from a former victim or from one of the aforementioned confederates, and early. Don't be stupid. Good luck.  more