The ACLU opposes these laws because they are both unconstitutional and ineffective as crime-fighting measures. 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, preventative detention invariable ends up being applied to many who would not have committed additional crimes if released, and releasing the few who are actually dangerous. 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 the other developed nations. In the past decade, more than 30 states have enacted mandatory sentencing laws requiring judges to impose stiff sentences for a wide range of crimes.