I've said this before, but I don't regard the death penalty as some inherently horrifying and barbaric sanction. The Japanese use it and whatever the flaws of their society may be, they don't strike me as a bunch of horn-helmeted pillagers and destroyers.
Even if we all accept this contention, the arguments against capital punishment remain far stronger than those in favour. It doesn't work as a deterrent and the chances of irrevocable injustice, while fairly low, are still far too high. I'd also add that many societies that embrace extreme punishments are also likely to embrace extremity in other areas of public policy, to the disadvantage of all.
The only arguments for capital punishment that ring true for me are the ones that Mencken cited back in the twenties - namely, that the death penalty satisfies the entirely natural desire of victims and their relatives for vengeance, and that the public's justified outrage is sated.
Even if this is the case - and it is, for many - these rationales are entirely undercut if victims have to wait more than twenty years for the deed to be done. Far from providing desperately-needed comfort, this merely drags out the agony for relatives who have to endure decades of legal debate.
It's a policy which manifestly achieves few of its alleged aims, so obviously that those who go out of their way to make claims to the contrary can be safely regarded as yahoos and conmen. See also, bloggers who make regular media appearances to act as slick salesmen for bullshit.