My friend Jason Brennan, a professor of philosophy at Georgetown, offers a short and sweet argument against the death penalty:
Even if we grant for the sake of argument that some people deserve to die, it does not follow that the state may be authorized to kill them. For a state to have the right to kill criminals, it must make decisions about guilt and hear appeals in a fair, competent, and reliable manner. It must have rules that reliably let the innocent–or those whose guilt is reasonably in doubt–go free. The American criminal justice system fails to meet these standards. Perhaps a government of smart angels should be granted the right to kill. We could debate that. But no state in America deserves any such right.
I think this is right. Indeed, this used to be my own standard argument against the death penalty. Its virtue is in its first step. The argument is neutral on the question of whether some people deserve to die. Now, I don't know when it happened, but at some point in the not-too-distant past, I stopped wanting to grant, even just for the sake of argument, that some people deserve to die and thus that perhaps it would be alright if a government of smart angels were granted the right to execute.
I think part of the shift in my thinking is a result of my research on the dramatic changes in moral culture that have come in the wake of technological progress and economic growth. (At one point, I was trying to write a book on this.) We have in fact become both smarter and more angelic and the result is increasing abhorrence of the death penalty. If we were smart angels, we would demand an end to executions.
I have here advance proofs of Steven Pinker's forthcoming book, The Better Angels of Our Nature: Why Violence has Declined. It's a smorgasbord of data on liberalizing moral change. Pinker shows that modernity brought about a stunning shift in norms, including attitudes toward capital punishment. Look (click to enlarge):
In the face of such a decisive trend in moral culture, we can say a couple different things. We can say that this is just change and says nothing in particular about what is really right or wrong, good or bad. Or we can say this is evidence of moral progress, that we have actually become better. I prefer the latter interpretation for basically the same reasons most of us see the abolition of slavery and the trend toward greater equality between races and sexes as progress and not mere morally indifferent change. We can talk about the nature of moral progress later. It's tricky. For now, I want you to entertain the possibility that convergence toward the idea that execution is wrong counts as evidence that it is wrong. This would suggest that those American states yet to abolish the death penalty are cases of arrested development. Looking at these trends, it seems overwhelmingly probable that we will look back on the death penalty as a shameful bit of lingering of savagery. And we won't be wrong. If our smarter, more angelic future selves wouldn't concede, even just for the sake of argument, that capital punishment is okay, why concede it now?