Paul J. Griffiths in Against Capital Punishment gives the following argument against C. P.:
The U.S. is a constitutional democracy, committed in theory to serve and protect the inalienable rights of its citizens, who are also its sovereigns. Those inalienable rights include the right not to be killed. A sovereign authority that permits or requires itself to alienate that right from any one of its citizens, for whatever reason, performs an incoherent act. It arrogates to itself the right to make exceptions to the universal economy of rights it theoretically serves, and thus makes itself sovereign over the economy of rights it is supposed to recognize, acknowledge, and serve. Dictatorships can coherently do this; constitutional democracies can’t.
Here is my pithy formulation of the argument. It is logically contradictory to maintain both that (1) the right to life is a unalienable and thus inviolable natural right logically antecedent to the state and its constitution, and that (2) the state has the right to violate the right to life as a punishment for certain crimes.
Edward Feser in Hot Air vs. Capital Punishment: A Reply to Paul Griffiths and David Bentley Hart is not impressed with Griffiths' argument:
Then there is Griffiths’ claim that, at least in the American context, when the state executes an offender it “performs an incoherent act.” How so? Because, says Griffiths, the American system is “committed in theory to serve and protect the inalienable rights of its citizens” and “those inalienable rights include the right not to be killed.” But there are at least four serious problems with this argument. First, it proves too much. While it is true that the Declaration of Independence refers to “unalienable rights,” and includes the right to life among them, it also includes the right to liberty. Hence, Griffiths’ argument, followed out consistently, would entail that in the American context the state performs an “incoherent act” even when it imprisons offenders, and indeed when it inflicts any punishment at all, since all punishments in some way or other infringe on an offender’s liberty. Presumably Griffiths would not want to do away with the entire system of criminal justice. In that case, though, he cannot consistently appeal to the Declaration as a justification for abolishing capital punishment, specifically.
Second, precisely because Griffiths’ interpretation would have such absurd consequences, it is hardly plausible to suppose that Jefferson and Co. meant for the term “unalienable” to be understood the way Griffiths understands it. Surely what they had in mind is the idea that an innocent person cannot have his basic human rights taken from him by the state. A guilty person, however, forfeits his rights by virtue of his offense, and for all Griffiths has shown, this can include the right to life no less than the right to liberty. (Indeed, the same generation that gave us the Declaration of Independence enacted capital punishment laws in every one of the original thirteen states and in the First Congress. The Bill of Rights itself recognizes that citizens may be deprived of “life, liberty, or property” as long as there is “due process of law.”)
Third, it is in any case far from obvious that the presence of these words in the Declaration would make the American system “incoherent” even if we accepted Griffiths’ interpretation of them. For while the Declaration expresses certain widely shared moral ideals, it does not follow that they have, simply by virtue of being in the Declaration, any legal or constitutional significance. While an explicit or implicit contradiction in the law itself would plausibly ground a judgment to the effect that there is “incoherence” in the U.S. system of criminal justice, a mere reference to widely shared and vaguely defined moral sentiments hardly provides a compelling argument.
Fourth, what matters ultimately is not what the Declaration says, but what natural law reasoning actually establishes. And what it establishes, as we argue in the book, is that an offender can forfeit his right to life, just as he can forfeit his right to liberty. Human law, including the American system of criminal justice, is answerable to natural law, not the other way around.
Feser 1 - Griffiths 0.