The desire for revenge in ye olde cavemanne times served as a rather crude way to ensure ones' safety. If you hurt a person, or stole their stuff, or burned their house down, or whatever, they'd go and kick your ass, or failing that, get the rest of their family to do it.
One problem with revenge is that it doesn't take much to create a cycle of escalation. Person A steals B's stick, B smashes A's possessions, A kidnaps B''s daughter, B kills A, A's family kills B and his family, etc.
Another problem is that it's comepltely unregulated. A percieved slight, even if unintentional, can start off a cycle rather like the one above. In addition, when one takes revenge, one rarely takes the time to collect evidence and witness statements, nor let the other party speak in their defence.
Justice is a better system by far (which is why we all use it). All the rules are laid out so that everyone knows what they can and can't do. Prosecution is limited to the individual who committed the crime, and nobody else has to get involved. Most importantly, it can settle disputes between two groups without resorting to the cycle of escalation, which in a society as large and connected as ours would likely prove quite destructive.
So no to revenge, I say. Unless you exist in a world where law and state have yet to form, it is not a valid way to settle disputes.
