KFunk said:
I agree with you on the last point, bringing us to the question: which point should we reject? The problem I have with rejecting point three is that its truth doesn't depend upon our acceptence (in the way many moral 'truths' may) because it rests on objective foundations. The general solution, to my mind, is to change the conditions for, and the motivations behind, punishment. You could use it as a deterent (as you have suggested) in certain cases or you could claim that people deserve to be punished if they commit wrong, even without being responsible for the actions (I am less inclined to agree to this latter point, as you have noticed). I don't oppose punishment in all cases, but I do oppose punishment which is particularly painful or prolonged. I find rehabilitation preferable (in an ideal sense) in most cases.
I agree on the distinction between moral 'truths' and objective truth. However, I don't feel that it is a valid general proposition, from a purely objective and consequential perspective, that ignorance of the objective truth leads to negative outcomes. On the contrary, ignorance of the truth may be beneficial on aggregate (economics and psychology would enlighten us on that issue).
I think we tend to underestimate the effectiveness of deterrence since we are generally law abiding citizens (education having a strong inverse correlation with rate of criminalisation). Now, think of a morally ambiguous crime with fairly poor levels of enforcement, such as illegal downloading of copyright music from the internet. I won't admit to anything, but it's fair to say that such laws would have far greater impact on changing behaviour if they could be widely enforced - if the deterrence effect is sufficiently strong. Another example is euthanasia, but I think this thread sufficiently touched on the issue.
Rehabilitation may be effective to an extent, but I think it's dangerous to overemphasise it. Sure, it may be an effective way to 'cure' the individual criminal - but only the individual criminal. At the same time, if we take away the emphasis on deterrence, the incidence of that crime within the broader community will increase. You have to take into account that, due to cost-constraints of the police force and the justice system, only about one prison sentence results from every thousand crimes committed. Therefore as primative as it sounds, there is a real need to 'make an example' of that offender.
Where rehabilitation is most appropriate, in conjunction with deterrence, is where the individual has a high chance of reoffending (although some would argue that the more cost-effective method is to lock them up for longer).
I agree with the other points to varying extents.