Americans rank crime among the most urgent of social concerns. Overflowing prisons and public outcry have led many to propose that the criminal justice system could control crime more effectively by focusing on dangerous offenders.

Recent social studies have suggested that serious criminality is highly concentrated and that high-rate offenders can be distinguished from others on the basis of prior criminal conduct, drug abuse, and employment record. Such studies urge judges to shift from rehabilitative sentencing to selective incapacitation, with longer prison sentences...