In a post at Progress Online Mark Rowney argues that, of five possible objectives for punishment of actions deemed criminal, 'only three are appropriate in a democratic society': these are public security (that is, preventing the criminal from doing more harm); rehabilitation (making the offender less likely to offend again); and deterrence (of others from committing crimes themselves). The two objectives that Rowney rejects are political control and revenge.
It is extraordinary that, discussing punishment, he should fail to mention what has always been regarded as one of the major reasons for it - retributive justice. This is not just the same thing as revenge. Punishment under the rule of law differs from revenge in - among other ways - not being administered by those who have been wronged by the offence, and in not necessarily being as severe as the offence itself. A multiple murderer will not receive a proportionate punishment, and in jurisdictions without capital punishment, even the murderer of a single person will not be executed. All the same, it is one mark of an adequate legal system to treat those who seriously violate the persons or interests of others as deserving to pay some sort of penalty. This is a distinct objective from public security, rehabilitation and deterrence, and to lose sight of it is to underwrite the idea of a noxious form of equality: one in which those who respect the rights of others and those who violate them should not be treated differently unless there's some social benefit to be derived from this.
If you think about him, in the news today, you'll see what's wrong with Mark Rowney's schema.