Hello Publius,
Welcome to TFP and congrats on your first post.
I can't say, as a philosopher (though what one does to earn this title I don't know), that I agree with your analysis of the situation but you do come down on the right side of the argument
On a light hearted note, I can
guarantee that CP does very little to
deter the sorts of crimes that CP punishes.
More seriously, I don't think the 3 and 1 analysis grasps the pro-CP position. For a start life long imprisonment is almost as certain to prevent reoffending as CP - we all like to think of Shawshank like escapes, but they are very rare, especially from max security. Also, the "value" of human life will be a central, and hence strong, part of any utilitarian argument for or against CP. Finally, I do not think that there is necessarily any 'eye for eye' or religious connotations here. The driving force of the pro-CP position seems to be that some crimes are so serious and terrible in nature that only the most serious of punishments will match it.
What I most dislike about this debate is the pleasure which many people seem to take in revenge. Be it painful deaths or rotting away in prisons for 23 1/2 hours a day. Before being able to decide whether CP is right or not you must decide what the penal system is for. In my mind it is to prevent reoffending until the prisoner has been rehabilitated. No revenge, no 'eye for an eye', no cruelty, no death. Anything beyond this, I believe, is cruelty for the benefit of those on the outside and that is as barbarous as the crimes we are punsihing.