According to a study, criminals are not so forward-thinking as to consider the punishment for their crimes:
The findings suggest that 76% of active criminals and 89% of the most violent criminals either perceive no risk of apprehension or are incognizant of the likely punishments for their crimes.
Of course, you could look at that the other way: Punishment acts as a deterrent for nearly a quarter of criminals and over a tenth of the most violent criminals. Of course, to really get their attention, the level of punishment may be such that it would be unconscionable. In any case, I find the lead-in to this to be problematic:
The tenet that harsher penalties could substantially reduce crime rates rests on the assumption that currently active criminals weigh the costs and benefits of their contemplated acts. Existing and proposed crime strategies exhibit this belief, as does a large and growing segment of the crime literature.
Actually, it can just as easily rest on the notion that a criminal in jail isn’t committing crimes against the general public while in jail. I’m not saying that I agree with this, but it’s there. As some proponents of the death penalty are inclined to point out, the only way to make sure that someone never murders again is if they are dead. It’s one of the reasons why death penalty opponents should vigorously support real life with possibility of parole sentencing.