Vengence is Mine, Sayeth the Volokh
Update: Oyster, in a comment below, provides a link to a VERY well written post by Hilzoy at Obsidian Wings, who further links to Matt Yglesias. Both are worth a look.
Hullabaloo, Steve Gilliard, and Majikthise all note a VERY troubling post by Eugene Volokh:

Something the Iranian Government and I Agree on: I particularly like the involvement of the victims' relatives in the killing of the monster; I think that if he'd killed one of my relatives, I would have wanted to play a role in killing him. Also, though for many instances I would prefer less painful forms of execution, I am especially pleased that the killing — and, yes, I am happy to call it a killing, a perfectly proper term for a perfectly proper act — was a slow throttling, and was preceded by a flogging. The one thing that troubles me (besides the fact that the murderer could only be killed once) is that the accomplice was sentenced to only 15 years in prison, but perhaps there's a good explanation.

He's talking about this:

An Iranian serial killer convicted of kidnapping and murdering 21 children was publicly flogged and hanged on Wednesday before thousands of spectators in this small Iranian town, 40km (25 miles) south-east of the capital, Tehran.

By the way: Volokh is a professor of consitutional law at UCLA. And he updated his first observations with this:

UPDATE: I should mention that such a punishment would probably violate the Cruel and Unusual Punishment Clause. I'm not an expert on the history of the clause, but my point is that the punishment is proper because it's cruel (i.e., because it involves the deliberate infliction of pain as part of the punishment), so it may well be unconstitutional. I would therefore endorse amending the Cruel and Unusual Punishment Clause to expressly exclude punishment for some sorts of mass murders.

Naturally, I don't expect this to happen any time soon; my point is about what should be the rule, not about what is the rule, or even what is the constitutionally permissible rule. I think the Bill of Rights is generally a great idea, but I don't think it's holy writ handed down from on high. Certain amendments to it may well be proper, though again I freely acknowledge that they'd be highly unlikely.

You know, I'll bet that deep down Volokh and the Iranians agree on more than just one thing.

It's easy to condemn monsters--and it's evident that it's just as easy to torture and kill monsters. It's a LOT more difficult to show a degree of, oh, I don't know, enlightenment and even adherence to civilized rules of law when dealing with them. But over time, some societies have, well, evolved to the extent that mature judgement--more or less--has superceded the notion of blood fued, straight revenge, the lynch mob, etc., despite Volokh's wishes. And that's a good thing. Because while I'm sure the professor would, if pressed, further amend his post to note that he believes that ONLY the guilty should be treated this way, the reality is that sometimes guilt "beyond reasonable doubt" isn't so clear. And what happens then? Would Volokh be willing to accept the blame--and the punishment--if "mistakes were made"? I doubt it.

Pain over the loss of someone you love eats away at you--and I can't imagine the suffering that results from the murder of a child. But this society made a very conscious decision, enshrined in the Constitution, and reflected in the judicial system, the statutes, and so on, that vengence is beyond the purview of the citizenry, and even of the state. That might not sit well with those hungering for payback, but it's a concept designed to benefit the larger social good.

If Volokh REALLY likes this aspect of Iranian justice, he should move to Iran. He definitely should stop teaching law school if he can't understand why the system in place here--rule of law, public trials with juries, and a prohibition on cruel and unusual punishment--even for monsters--is, well, enlightened self-interest in action on a societal level.