I tend to think the answer is evidence-based reform. Check out what works and do more of that. As far as I can tell, the best results are had by rehabilitation type systems.

* What I mean by this is it might be a tautology that someone locked up in prison forever can commit no more crimes, but I'm not sure it's as simple as that. If you lock someone up:

a) You deprive their community of that person. Maybe their children will now become criminals.

b) You deprive their community of their spending power and work. Maybe it will become poorer.

c) They have the chance inside prison to share experiences with novice criminals and teach them how to become old hands, increasing crime when their cell-mates get out.

Now if that person is a negative on all the above values, maybe there is a point in not letting them out. Maybe they have broken homes, never work, and teach others about crime anyway. But that's not the person I'm comparing them to.

I'm saying the criminal in their community has a negative effect on society. Putting them in jail makes it zero. Actually rehabilitating them makes it positive.

If we could get rehabilitation to work, everything gets better. Personally, I think evidence from round the world suggests this is possible.