With only a couple of reservations, I don't have too much of a problem with the notion of capital punishment. I think it sits ill in the mouth of someone who has murdered, perhaps in a grotesque fashion, to complain about infringements of their human rights. I think it equally self-serving for those who have destroyed the lives of others, through excesses of violence or unwillingness to respect others (here I am thinking of those who peddle drugs on the scale enaged upon in The Wire), to cry about their human rights. Maybe it isn't an effective deterrent, maybe it does have an aspect of revenge about it, but these arguments are insufficient to change my view: I don't think it turns society into a murderer to deal to such criminals in such a final way, and the one clear thing is they won't be doing it again. And I am not convinced that making someone languish in jail for a lifetime is any more humane than giving them a quick end.
One reservation is that the criminal justice has to be sufficiently effective in its operation that we can be sure the guilty are those who are convicted. Even then, I'm not sure it has to be 100% effective: there is much rhetoric about it being better that 99 guilty go free than to punish one innocent, but it only takes one of those 99 to kill an innocent and we've gone backwards. A second reservation is that whenever we kill someone, others will be affected. The criminal won't have given them much thought, but the presence of his or her family and friends might give reason to pause. My other reservation is that any method used to carry out the sentence must be humane: there shouldn't be massive periods of waiting for it to be done, and the final process should be as peaceful and dignified as possible - to avoid any possibility of "us" taking pleasure in the process. I couldn't hope for a better person to conduct this service on society's behalf than Albert Pierrepont, at least as portrayed by Timothy Spall in a recent movie:
Pierrepont was the last British executioner. He was appointed not long before the beginning of World War Two and stayed in the position until the mid 1950's and, according to the film (there seems to be some variation) carried out 608 sentences. This film is largely focussed on him in his professional capacity: about the only things we learn of his home life is that he never takes anything of his work home (he needs this separation to stay sane) and that he does a bit of amateur stand up comedy with his mate Tish. He was a master of the measured drop - tailouring the length of rope needed to ensure that death was painless and immediate. The only mode he adopted was one of dignity (the one odd note struck was his competing to be the fastest hangman): it was not his place to judge any of those he met professionally and, once they were deceased, they were to be treated as having atoned for their sins and thus innocent once again. So, any failure to respect their corpse was wrong, such as when there were insufficient coffins. This was in the aftermath of World War 2, when he was sent to Hameln in Germany to hang war criminals, including the so-called Beast of Belsen. Here he had a long schedule of sentences to carry out (one source says there were 190 in all).
This was the beginning of the end for him: the deaths started to trouble his conscience, and I imagine that once one such death starts to intrude, each subsequent death becomes a further burden. We are not shown much of this: instead, the last straw comes when Peirrepont is called upon to hang his friend, Tish. The movie shows Tish as being comforted by the fact it is his friend who carries out this last task for him; Pierrepont for once drops his professional mask to give his friend some words of farewell but he can no longer perform his task. Finally, we see his demeanour crack, and it is revealed to us that he has felt tortured for some considerable time.
One other factor was the growing sentiment in Britain that hanging was to be abolished: there were public protests, accusations that he had blood on his hands. In fact, Time magazine has it that it was the British Parliament decision to do away the death penalty which saw him lose his job.
I doubt that many will choose to see this film, which gives an unusual insight into the process of capital punishment, but it certainly provides a good model for those societies which decide to use the process.