Dr Alan Stone (1982) gives a list of adverse social consequences of civil libertarian and progressive reforms in American law and psychiatry. I shall not try to deal with his critique as a whole: of his ‘bill of particulars’ I shall attend only to the question of protecting the public. The concept of dangerousness is the villain of his piece and I shall consider it in social perspective by offering some observations on the notion of protecting the public and on the suitability of clinical assessments of dangerousness as instruments of public policy.

There is today a tension at the heart of public policy: protecting the public indirectly from the risk of grave harm at the hands of mental patients and serious offenders, by hospitalising and imprisoning them for long periods, frequently exposes those sentenced to the risk of unnecessary detention – unnecessary, that is, for the avowed purposes of treatment or punishment. Wherever the movement to block this source of injustice has been successful, the authorities have thought it necessary to make special arrangements to identify and detain a minority believed to be dangerous. But the practice of detaining people on a presumption of dangerousness carries its own risk of infringing the rights of mental patients and serious offenders; for a high degree of uncertainty is inherent in predictive judgments of conduct, and preventive measures taken on the basis of such judgments impose on those to whom they are applied a correspondingly high risk of being detained unnecessarily. The practice therefore comes under attack from reformers, who say it should be abandoned.