The state should not kill a person once that person no longer poses an immediate threat to society.I also stated why this "argument" wasn't much of an argument, and I identified what I thought were some obvious problems. The chief problem was that I believed (and still believe) it to be a "question-begging" argument: if one already agrees with it, then one probably does not need to be convinced that the death penalty is wrong.
What I didn't do is explain further why I don't try to convince people of it. What are the reasons behind my saying that the state ought not kill those whom it has neutralized? I could cite some of the reasons that Pascal-Emmanuel Gobry tries to "demolish" or at least offer rejoinders for--the near certainty that some mistakes will be made (he did, after all, write this in response to the outcry over Troy Davis's execution) and that the death penalty might not operate as a deterrent (although I personally find this argument unprovable and based on assumptions about the purpose of punishment that I do not necessarily share). I also would add the alleged--and to my knowledge well-backed up by statistics--race, class, and (I suspect) sex discrimination* when it comes to who gets executed. There may very well be other reasons, some of which boil down to "I don't want to trust the state not to mess it up." As reasons, they have a certain force, and if true, might lead anyone to oppose the death penalty as a practical matter even if they support it in theory.
The truth is, however, that none of these reasons constitute my true rejection. All of them could be shown to be based on false premises--or could be stipulated to be false--and I would still oppose the penalty. In short, to adopt those as the reasons I oppose the death penalty--even though at least some of them might be sufficient reasons in themselves--would be dishonest on my part.
In short, my "argument" is not an "argument." I cannot use it to convince someone who doesn't already agree with me. I do not expect someone who is pro-death penalty to hear my "argument" and change their minds because of it. I might try to convince them that they already believe, deep down, that the state shouldn't kill people that do not pose an immediate threat. But such convincing would be a different feat, an act of showing that my opponent is actually someone who agrees with me already, not someone whom I could convince.
*When it comes to this point, I know nothing for certain. I suspect--and it's only a suspicion, founded on nothing--that if a similarly situated man and woman commit the same type of capital crime, then the man would most likely receive the death penalty. Again, I have no evidence, and I acknowledge two points. First, women often are and have been executed. Second, I understand that men tend to commit more violent crimes than women do, so establishing a way to test my suspicion systematically is quite hard.