Gov. O'Malley on the death penalty

A few days ago, Gov. Martin O'Malley of Maryland had this op-ed, "Why I Oppose the Death Penalty," in The Washington Post.  The piece seems informed by O'Malley's understanding of, and engagement with, the Church's evolving position on the issue.  He writes:

In evaluating whether Maryland's criminal death penalty should be replaced with life without parole, one must be guided by the answers to two basic questions:

· Is the death penalty a just punishment for murder?

· Is the death penalty an effective deterrent to murder?

O'Malley appears to assume that the answer to the first question is, in some cases, "possibly, yes."  But, he then refines the question, and asks whether, "[n]otwithstanding the executions of the rightly convicted, can the death penalty ever be justified as public policy when it inherently necessitates the occasional taking of wrongly convicted, innocent life?"  And, in answering this question, O'Malley turns to the question of deterrence:  "Does the use of the death penalty -- while rarely, if ever, 'just' -- save more innocent lives than it takes?"  Finally, he concludes with this:

And if the death penalty as applied is inherently unjust and lacks a deterrent value, we are left to ask whether the value to society of partial retribution outweighs the cost of maintaining capital punishment. While I am mindful of and sensitive to the closure (and in some cases the comfort) that the death penalty brings to the unfathomable pain of families that have lost loved ones to violent crime, I believe that it does not.

Human dignity is the concept that leads brave individuals to sacrifice their lives for the lives of strangers. Human dignity is the universal truth that is the basis of ethics. Human dignity is the fundamental belief on which the laws of this state and this republic are founded. And absent a deterrent value, the damage done to the concept of human dignity by our conscious communal use of the death penalty is greater than the benefit of even a justly drawn retribution.

While, in the end, I share Gov. O'Malley's view on the "policy question," I'm a bit uneasy with a few of the moves in his opinion piece.  Or, maybe I'm just misunderstanding.  It is not entirely clear to me what "work" O'Malley's claims about deterrence, cost, and risk-of-error are doing with respect to the "is the death penalty just?" question.  Now, certainly, if we are consequentialists, the question whether the death penalty's costs (money & risk of wrongful executions) outweigh its benefits (closure for victims and deterrence) is an important one.  But, does O'Malley think that "the concept of human dignity" precludes capital punishment or not?  If it doesn't, then would it matter if the death penalty could be administered less expensively, or if we had good data on deterrence?