God said, "Thou shalt not kill" ... If it's said that this commandment applies only to illegal killing, what's to prevent human beings from similarily agreeing among themselves to legalize certain types of rape, adultery, or perjury? Considering that God has forbidden us even to kill ourselves, can we really believe that purely human arrangements for the regulation of mutual slaughter are enough, without any divine authority, to exempt executioners from the sixth commandment? Isn't that rather like saying that this particular commandment has no more validity than human laws allow it? - in which case the principle can be extended indefinitely, until in all spheres of life human beings decide just how far God's commandments may be conveniently observed.- Rapheal Hythlodaus in Thomas More's Utopia (Penguin Classics pgs 28-29).
Close to five-hundred years ago Thomas More offered those arguments against the death penalty in Utopia, and though some of them are laced with religious terms, I argue when one considers modern notions of morality and justice, including equity, it can be seen his arguments not only extend to present day, but remain impressively strong.
Firstly I believe that no devout Christian who operates within reason can refute More's arguments and thus maintain to be a proponent of the death penalty.
Of his arguments the one that struck me, in referencing the 6th commandment, was, "If it's said that this commandment applies only to illegal killing, what's to prevent human beings from similarily agreeing among themselves to legalize certain types of rape, adultery, or perjury?"
This argument against the death penalty uses the important idea that there are things we all know are wrong, not in the illegal context but wrong outside of any legal considerations; it is premised that murder, rape, adultery, etc. are examples of these.
More's argument proceeds from the common idea that killing is an extreme wrong and goes on to conclude that in legalizing killing (the death penalty) a country allows for all other wrongs to be legalized, in particular those of a more heinous nature.
To put it in other words, if a state was to kill someone for killing someone else there must necessarily be the initial idea that killing someone is supremely wrong to attempt to justify the death penalty. That idea of course has the clause though that it's okay for the state to do if enough people agree to it. From that it is reasoned, if killing people is extremely wrong, but the state can do it if the majority allows, then it must necessarily follow that extreme wrongs can be done by the state if any majority consents.
Those who are for the death penalty must answer how it would be okay for them to legalize killing, but not for another majority to legalize rape, when both are extreme wrongs. One can certainly imagine, albeit a hopefully far-fetched, emotional majority sanctioning rape as a punishment for a rapist, and in such an example how would those who are pro-death penalty say that particular majority is wrong? For if they don't they are sanctioning cruel and unusual punishment, something they have hence philosophically avoided with the introduction of lethal injection (I will assume I do not have to show the immorality of such a sanction). But if they disapprove of rape for the rapist they are saying that one majority is right and another is wrong which cannot be justified in terms of their argument.
Thomas More's argument not only provides a frightening conclusion which showcases the powers those who are for the death penalty offer the state, (powers to commit, from their own argument, an extreme wrong), but also highlights the contradiction in their position that suggests only their majority has the right to commit an extreme wrong.
We all know killing is a grave wrong, and that's why we seek to punish those who do. For punishment some suggest the state should kill, in doing so they ignore the fact that once you allow the state the ability to commit one evil, you give the state the ability to commit any evil. Once one majority sanctions one extreme wrong, any majority is given the the ability to sanction any extreme wrong. One must then pity the minority in that state where natural law is disregarded, for even the constitution and obedience to it would be at the majority's whim.