However, when considering as big an issue as this I feel it is important to detach somewhat emotionally to review all of the related factors and issues. I then think its good to put the emotion back in to 'test' how the rational conclusion feels.
The factors I feel are core to this debate that I will discuss here are: safety of convictions, deterrence, human rights, state power and justice.
Safety of convictions
For me this is the deciding factor. I am against the death penalty. The risk of convicting and executing an innocent person is, in my opinion, not worth any benefit that having the death penalty may bring. Unforunately, that risk is great. Forensic science, though fantastic, is still flawed. In the UK (and the US) there operates an adversarial system of law which further contributes to an insecurity in convictions.
I cannot envisage a time where enough convictions could be 100% certain to justify a death penalty without infringing very greatly upon the civil liberties of us all.
Many people argue that having the death penalty deters people from committing crimes. However, studies have shown that this simply isn't true. In countries with the death penalty crime and murder rates are no lower than in countries without - indeed, some have even higher crime and murder rates. In addition the studies show that the death penalty offers no greater deterrence against crime than life imprisonment.
This information shows that in the US states with the death penalty actually have a consistently higher murder rate than states that do not have the death penalty. Some criminologists argue that the death penalty has a brutalising effect on people, thus creating a more violent society.
Human rights are often denigrated in our society as the preserve of the 'loony left' that continually stop justice from being done. In my view human rights are important. Human rights are what help guarantee us all a basic standard of living and of security from the state. To deny one section of human rights is to devalue the meaning of those rights for th rest of us.
The issue of state power over its citizens is a pretty big one for me. In the UK we are lucky that while we may often be dissatisfied with our government it does not terrorise us. When considering how quickly other liberal democracies have fallen into totalitarianism it is my view that it is best not to advance things which could make this process quicker or easier. This is not a paranoid stance. I believe in a limited state and a larger private sphere. Things like the death penalty (giving the state a right to murder its citizens) impact on this.
In a situation of a corrupt government and a corrupt judiciary having the machinery for state execution in place (perhaps initially with public support) wouldn't be a good thing.
Many people argue that the only way for there to be real justice for victims of horrendous crimes is for the perpetrator to be executed. I fully understand that perspective. I often get an emotional response in the same direction when I hear about horrible things: I would argue its a somewhat natural human reaction to horrendous things.
However, that doesn't make it the most healthy thing to do for our society. Execution does not reverse the crime or make anything materially better for the victim or the victim's family. In my view ensuring that the perpetrator is removed from society and does not have the freedom to hurt more people should be the core issue. In the case of severe crimes life long imprisonment without parole would serve this purpose. Revenge is tempting but overall not productive.
Perpetrators of horrendous crime should be locked up for the rest of their natural lives. The risks of executing innocent people, sacrificing the human rights of all and giving the state too much power are too great to justify urges for revenge and a disproved deterrence effect.