As Burnsy pointed out, there are three main purposes for having a system of justice, but I would add a fourth to the list. They are:
1. Public safety.
2. To rehabilitate.
3. As a deterrent.
4. As punishment
I want to argue that retributive justice (i.e. # 4 above) is founded on old-fashioned religious views, and that as such, we should abandon it altogether. I also want to argue that if retribution has any effect on the offender at all, then it surely falls within the scope of points 1, 2 & 3 above, thus making retribution for its own sake unjustifiable and unnecessary.
So what exactly is the underlying notion of 'justice' within 'The Justice System'? The majority of people would claim that it has something to do with "punishing the offender" or "making them suffer for the suffering they've caused". This idea is more simply known as 'an eye for an eye'. It has its roots in an unenlightened worldview where the ultimate judge, jury, and executioner is a bearded white man in the sky. It gains its authority as a system from the authority of God, rather than its usefulness on Earth.
Most people will argue against this in the following way: It is only human nature to want to avenge wrong-doings, and therefore retributive justice reflects human nature. However, our systems of evidence, impartiality of police, courts and juries etc. all point to the fact that humans have developed past the point where we simply follow vengeful urges. There is a contradiction here in that we take impartial and terrestrial ownership of the evidential side of justice, but we then look to the 'human nature' model or the Divine model for guidance on how to proceed after we have collated the cold hard facts of a case.
We should instead be looking at the cold hard facts of retribution in terms of real-world usefulness. What we find if we do, is that punishment can be explained as numbers 1, 2, and 3 in the list above.
In short, retribution for its own sake is extremely difficult to justify without using words like 'deserve', or 'ought', or 'evil'. Explanations of these words invariably appeal to human nature or God for their authority (have a go try to explain them without using those two anchors...). The justice system is set up exactly to prevent the retributive part of human nature. It is also set up to hasten (presumably an infinitely long wait for) Divine Judgement.
Edited by Bouquaine, 03 October 2011 - 04:34 PM.