Prof. Joseph M. Bessette has this article with the above title in the Catholic World Report. The article is partly a Catholic theological argument, but it is also an empirical argument on deterrence.
Examples such as these powerfully refute the claim that the death penalty never deters. Though many large-scale empirical studies have purported to find a substantial deterrent effect (as we detail in our book), others have challenged these findings, and among quantitative social scientists the issue remains unresolved. But this should not surprise us at a time when executions per year (51 between 2000 and 2015) are dwarfed by homicides per year (15,600 during the same period). Even if each execution saved 5-10 lives (a midrange for the studies that reported deterrence), the total number of lives saved would amount to only a few percent of all homicides. It is simply not likely that social scientists could discern such a statistically small effect, especially when year-to-year changes in homicides are driven by a host of social conditions independent of punishment practices: drug use, gang wars, economic conditions, immigration patterns, etc. Yet, even a small deterrent effect (say in the range of 2-3) would have saved several thousand lives from the nation's 1,465 executions since 1977. And of course if the death penalty does deter, it would save more lives if it were used more often.Thanks to Dudley Sharp for the link.
No rational argument can be made that the DP does not deter murder. The idea that NO potential killer has left his gun at home, or not loaded it, when he was planning his convenience store robbery (or his drug deal collection or his revenge against his neighbor) -- and has taken this precaution for fear of the DP -- is preposterous.
The question that can realistically be debated is how MUCH deterrent value the DP has. Reasonable minds differ on that, but two things are clear: That it has some degree of deterrent value, and that it would have more if it were imposed more often.
OF COURSE there is a deterrent effect. Both animals with an adequate IQ and humans look to avoid pain and punishment.This is backed up by every study from rats getting shocked by electricity instead of receiving a food pellet to human studies. This truth does not suddenly stop at the DP. As Bill states, it is merely a question of how much it deters.