Doggoneit, Tom's making me have to dust off the cobwebs from that section of my brain I haven't used since I got my undergrad degree in Religion. Anyway here's a quick riposte to his post:
I disagree with your contention that current Church teaching is utilitarian. I think that the element missed in that sort of analysis is the option of salvation. As long as someone lives he has the option open and a just people (who are protected) has a duty toward this salvation. Since acceptance of punishment is viewed as cleansing, maybe the Catholic position should be life in prison with the ability to accept the death penalty in order to absolve one's soul.
And now let's open another can of worms. Are you of a mind that you divide the magisterium into ordinary, ordinary universal, and extraordinary? If so, yes the various authorities you cite are ordinary. Under that sort of analysis, everything which has some support among some members is ordinary; of course, it would not be infallible.
I don't think support the death penalty can be a core universal teaching for an organization dedicated to extending the salvation of Christ's sacrifice to each of us. It can be an (or the) accepted necessary punishment to protect or to save (with acceptance by the sinner) but extending it beyond that doesn't make sense.