I think a lot of people will behave in ways that they think is expected of them. So, if people think criminals are criminals and cannot change, then they will be unlikely to change.
If a criminal committed their crime for understandable reasons then I think they can be rehabilitated. For example, if a mother defended her children by killing an aggressor, then she is not a cold blooded murderer who cannot be changed. But if a psycho killer kills 20 women, then he is unlikely to change.
Rehabilitation is an important part of a civilized society. If we abandon that idea, we are abandoning our civility.