I don't agree that prevention of future nonviolent crimes is a mandatory goal. Think about a routine drug user. It is a crime, but I am not willing to imprison someone just for repeating that crime. Some crimes just don't have enough social impact. It is unjust to viciously enforce compliance simply because some behavior is illegal.
Nonviolent != victimless. My point is not about 'should X be punished' but 'how do we handle definitely punishable small crimes repeated ad nauseam'.
Think about a routine drug user (say, heroin addict) who regularly (daily/weekly) performs theft to sustain the habit - car radios, shoplifting, maybe an apartment if he gets a chance. It is a very common scenario in many places, if the user can't quit (or always restarts a few months after therapy/quitting) and the needed drugs are all illegal & expensive; as the only real non-crime [here] alternative they have is prostitution and many of them consider theft as the more pleasant option.
Even a small, friendly village community who know everyone and help each other would likely vote [for laws] to imprison him in order to stop the behavior. Rehabilitation is another option, but the idea is that after 3-strikes you have to admit that your rehabilitation (however good or bad it is) doesn't work and you have to do something else.
Or think of a genuine kleptomaniac. Unless it's successfully treated, you still need to take some measures to prevent repeated crimes.
