I've disagreed with people before on this topic; I feel that the primary goals of the system should be rehabilitation (so that society can make productive use of former offenders) and deterrence. I've discussed it with people who seem to argue the primary goal is punishment - perhaps this is intended to work as deterrence, but it's clear that this is not the case. A "you were bad, now you get punished" mindset seems to be at work, rather than one seeking to solve the issues. The notion that people who committed crimes should not be allowed to learn new skills or seek ways of bettering themselves because they are being punished is not uncommon, even though this removes an opportunity for people to try and get out of a criminal lifestyle.

On the other hand, recidivism is pretty high in Ireland, and I've heard that here and elsewhere, prison is practically a criminal education centre. Sentences are often inconsistent - I'll try find some examples of weird sentencing - and often cut short.

The only conclusion I can draw here is that current system is a total mess, and needs significant overhaul.

I'm okay with capital punishment for particularly serious crimes. There was a good post on this recently.

Final point: I've heard it said (though cannot find figures on this) that in parts of the US, the time spent waiting on death row is so long, that your life expectancy is higher if you murder someone when you're in your early twenties than if you stay on the streets. Interesting that choosing execution could be seen as a rational choice.