What kind of revenge are we talking about? Most of the times I'll let things play out themselves but there are the extreamly rare times where a punch to the jaw is in order.
Hitting someone in today's world, even if that person just committed a crime, could end up in a lawsuit, with you at the wrong end of it.
IN NYC a criminal in the process of running from the cops was stopped by a taxi driver. The criminal was arrested AND AFTER HIS TRIAL WAS FOUND GUILTY. He, in turn sued the taxi driver who purposely hit his get away car.
Some IDIOT lawyer took the case, Some idiot judge heard the case, and found for the criminal. Political Correctness, trumps, common sense and common decency every time.