I agree, In some circumstances some people have a right to take vengeance. but, I will say, That's self-defense, not vengeance. Self-defense is human right, everybody's way of self-defense is different. strong people do self-defense by violent way, stronger by mind-game and strongest people, we call them prophets, If somebody did bad, in return, they do good with him and realize bad person his mistake and they also show right path to them. at last, everybody's strength is different, so way of self-defense differs.
I only take vengeance if the respective person has wronged me very, very much. In this case, they shouldn't be left unpunished. They will never learn their lesson. But most of the times, I have only had to deal with ephemeral stuff. I know people who would take vengeance on my cases if they were in my place, but I'm not that kind of guy.