World: Why capital punishment is a crime

As I understand it, the main arguments in favour of capital punishment are:
1) Preventing recidivism (re-offending);
2) Deterrence;
3) Vengeance.

Five arguments against capital punishment:
1) It further brutalises society - and those directly involved;
2) The occasional possibility of killing someone innocent;
3) It offers no opportunity for repentance;
4) It offers no opportunity for forgiveness;
5) Studies tend to show there is no deterrent effect (see adjunct discussion* at bottom).

If you consider the option of life imprisonment, the only pro-death point left is vengeance. I would argue here that this solution is not the hallmark of a mature civilisation.

This has been in the news in recent times in particular due to the sentencing of several Australian citizens in Asian countries for smuggling drugs (specifically, in Singapore and Indonesia). Those people were young, stupid and desparate rather than hardened criminals. Don't get me wrong: I'm not favouring Australians above anyone else, nor denying the ravaging effect of hard drugs. In fact, a heroin drought in Sydney in the last ten years was credited for a drop in crimes such as burglaries and robberies. [per the NSW Bureau of Crime Stats. Its inestimable director Don Weatherburn frequently adds a rational perspective to the tabloid debates to which Sydney is prone.] So the less trafficking the better.

At this point I find it hard to disentangle broader aspects of ethics from the Christian ethos that imbues modern western civilisation. Specifically, are notions of forgiveness and repentance very particularly Christian, or can it be argued that they form part of a higher ethical philosophy? I believe that the practice of repentance and forgiveness more demonstrate an abstract philosophical maturity than simply reflecting christian morality, but I can offer no immediate arguments in favour. Comments are welcome.

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*Blumstein, and Block (below) are examples that show no deterrent effect. All studies that I have seen with opposing conclusions (such as Dezhbakhsh) simply use statistics on changes in murder rates. This doesn't take sufficient account of other factors (eg increased lockups due to the "zero tolerance" regimes). In effect, "all other things not being equal..."

References:

• Block, Eugene B.. When Men Play God: The Fallacy of Capital Punishment. San Francisco: Cragmont Publications, 1983
• Blumstein, Alfred and Jacqueline Cohen. Deterrence and Incapacitation: Estimating the Effects of Criminal Sanctions on Crime Rates. National Academy of Sciences: Washington, D.C., 1978
• H Dezhbakhsh, PH Rubin, JM Shepherd: Does Capital Punishment Have a Deterrent Effect? - American Law and Economics Association, 2003