 A finding of "mental illness" alone cannot justify a State's locking a person up against his will and keeping him indefinitely in simple custodial confinement.Assuming that that term can be given a reasonably precise content and that the "mentally ill" can be identified with reasonable accuracy, there is still no constitutional basis for confining such persons involuntarily if they are dangerous to no one and can live safely in freedom.The origins of Donaldson's institutionalization began in 1943, at age 34, when he suffered a traumatic episode.