criminologists say it's the certainly of punishment, rather than the severity of it, that is the deterrent. In fact, I believe, most criminals just grow out of it. By far the biggest criminal demographic is young males; and most of them grow up, acquire responsibilities, and go straight. You could dramatically reduce crime by locking up every 18-year-old male until he turned 30. But that would also cause proportionality problems, I suppose. (And seriously inconvenience a lot of young women.)