I do agree that revenge can be used to create a form of justice, but I do not believe justice should be based on or functions under a paradigm of revenge.
Well, not every crime is committed by a person who needs to be rehabilitated, so clearly rehabilitation can't form the basis of our justice system. A man who steals cars after a life of poverty and desperation and a lack of employable skills surely needs rehabilitation and training in useful skills.
But the man who, say, loses his job unexpectedly, finds his car damaged in the parking lot, goes home early and finds his wife in bed with another man - snaps - and commits a murder? Rehabilitation? It was a crime of passion, a once-in-a-lifetime mistake he's not likely to make again. Does he need to be rehabilitated? Of course not. But he does need to be punished; revenge needs to be taken for the victim.
We have a saying - "the punishment should fit the crime." What is that if not a statement of proportional vengance?
No matter who you kill, if you kill then you are a threat and need to be dealt with to reduce that threat.
In what sense a threat? Just because one kills, doesn't mean one is going to kill again. There a many murderers we certainly don't expect to kill again.
Some murderers have no need for rehabilitation, and we have nothing to fear from recidivism. We punish them anyway out of vengance for their victims.
I see what you are saying and it could certainly be viewed that way.
I think we're both right. Justice can be rehabilitating; it can be a tool of vengance, too. I guess in a democracy we can craft our laws to suit both purposes.