Locking up criminals should be for the benefit of society at large. People can change, sure, but the state can't change a person's heart in a reliable fashion. It can only make the path of crime painful and isolate those who choose it from society.
For instance, toleration of robbery only leads to more robbery, as long as the robber suspects that he'll benefit on net. From the victim's perspective, it's an easy wrong to make right, though. The victim just wants their property back.
I've found the opposite a lot of time. For a lot of first time victims, especially of robberies or burglaries, the loss of the feeling of safety in their home/car/person is a lot more significant to them than just getting back whatever was stolen. One of the big theories in restorative justice is that being able to talk with the defendant and understand them would help them get over the trauma of being victimized as much as it would help the defendant.
As for its effectiveness, its very limited. There are plenty of victims not interested in reconciling with defendants whose primary goal really is for the state to punish the defendant. There are also plenty of defendants either openly uninterested in dialogue about what they did or only interested in the parts of the process that see them out of custody or probation sooner with no real desire to change. In cases involving domestic abuse it can be an actively harmful process, giving an abuser another chance to manipulate and gaslight the victim into going back to a bad situation. Of the cases I've referred to a restorative justice program most were unsuccessful.
I've had several thousand cases as a criminal attorney. Maybe a few dozen were appropriate for restorative justice. Probably a dozen of those actually went through the process. Most of the successful ones involved juvenile defendants. That's where I think it shows the most promise.
