The purpose of bail is not to punish, but to guarantee a defendant's presence at trial. Although we've all heard lurid stories about the accused rapist who, freed on bail, goes forth to commit another rape the same day, such occurrences are really the exception rather than the rule. In a 1981 U.S. Department of Justice study of eight sites around the country, only 1.9 percent of all defendants released before trial were later imprisoned for serious crimes committed while out on bail. The second assumption is even more faulty. Neither judges nor psychiatrists can make accurate forecasts of future dangerousness.
Human behavior is just too unpredictable.
In practice, preventive detention invariably ends up being applied to many who would not have committed additional crimes if released, and releasing the few who are actually dangerous. Pre-trial detention is a profoundly antidemocratic measure that does not work. Behind the myth that judges are too soft-hearted in their sentencing practices lies the reality that people are too often deprived of their liberty. The United States imprisons more people per capita than any other industrialized country except South Africa and the Soviet Union. And harsh sentencing is now the rule, with American sentences tending to be much longer than those imposed for similar crimes in other developed nations.