“Utilitarian?” How does that term even apply here? Utilitarianism is essentially social hedonism . . . do whatever makes the largest number of people feel good. Quite possibly this would just tick everybody off, especially the types that think justice = revenge. Do you mean, maybe, practical? Even the term “pragmatic” doesn’t apply here, because I’m not claiming “this is what works, so we should do it,” I’m saying, “here’s an abstraction derived from evidence, and you have to decide what to do based on the abstraction that corresponds to the evidence.”
I misread what you had originally written. I thought that when you wrote about keeping criminals from doing a crime, you were talking about punishing them to deter others, not to keep the same one from doing it again. Who are you claiming are violent criminals? Murderers, rapists, terrorists? Who else? Do you advocate that any person who is a violent criminal should thus be put to death, since there is no hope of rehabilitation? Also, I don’t think it is statistically true that no criminal who commits a violent crime can be rehabilitated, though I am sure that the number is quite low. For instance, a man who kills another man he just walked in on sleeping with his wife would probably realize the wrong he comitted instantly, and once he served his prison time (if he has the chance for parole), he would more than likely never do such a thing again.
Social hedonism is one version of utilitarianism, but the most general case would be to do the most good – however you formulate it – for the most people. Some utilitarians say that what is good is pleasure, and are thus hedonistic. But you can hold as your standard of good to be human life, and thus to do the most for people’s lives would also be utilitarian (note: I am not claiming here that the Objectivist ethics is in any way utilitarian, since the standard of good is MY life, not simply human life).
If your purpose of punishing a criminal is retributive – giving him what he deserves for his act – then you are appealing to a notion of justice. If the purpose of punishing a criminal is to try to keep others who are considering comitting a crime from doing it, then you are appealing to a notion of deterrance. Deterring individuals from doing a crime promotes good for both the potential victims and criminals, and thus it can be said that your system is utilitarian.
Deterrence is a ridiculous issue to even bring up; as I pointed out earlier it doesn’t do any good anyway.
Thiefs often make the decision not to rob a place armed with guns, since the punishment associated with bringing a gun to the crime is much higher (in some jurisdictions, it used to be punishable by death, in fact). For many criminals, no cost-benefit analysis is ever made, and these will probably not be deterred by much. But some criminals do think about their crime a lot before comitting it, and a stiffer penalty may deter them. It is not ridiculous to talk about it.