I remember once seeing a news story where someone who had just gotten out of prison murdered someone. People in the comments were saying he shouldn't have been let out. How after years in prison, of course he's going to be dangerous. Gotta love when the tough on crime people accidentally realize the futility of the prison system.

The goal SHOULD be to make criminals into productive members of society. Unfortunately, the actual goal in many places is to make criminals keep reoffending to make more money for the business of incarcerating people. Or sometimes the goal is just to punish, with no thought about the long-term utility. Some people just think some people deserve to suffer and don't care about the utility for society. It's the same reason they oppose social safety nets.