I used to be for capital punishment until I realized the degree of dishonesty and incompetence employed in the building of many cases against individuals by both law enforcement and prosecutors. One innocent person going to prison is one too many for me. But then I'm a perfectionistic prick who demands competence or get the fuck out of your job.
That could result in miscarriages of justice in the form of executions but it could result in people walking, in the UK it'd probably result in the department of public prosecutions saying that they could not be sure of a conviction on the basis of the case presented or the evidence and they therefore would not prosecute.
I've no love for the death traders and I'm glad when I hear the fate of violent offenders who are released after sentences and shot at the gate sort of thing (that's happened here at least). However, ultimately, the most important thing is that they are taken off the streets and for the duration of their incarceration are not going to be able to carry on with further and further offences.
I dont really believe in rehabilitation, in most cases anyway, its about securing convictions of criminals quickly when they are caught and therefore stopping the criminal behaviour.