One Flew over the Cuckoo's Nest
2. I do not think that McMurphy (Mac) was voluntarily committed. Someone who is voluntarily committed is a person who seeks help on their own. They check themselves into an institution and may leave whenever they want. Civil commitment is when a person is committed against their will. This happens when it is found by the court that a criminal is judged to be mentally ill and are a threat to others and they can be institutionalized against their will in place of prison.
Criminal commitment is when and individual has been acquitted of a crime by reason of insanity and are placed in a psychiatric facility for treatment. I feel that Mac was institutionalized by civil commitment. If he had not gone to the ward he would have been in prison. He was not acquitted for his crimes, he was sentenced to a work farm and they thought he may be faking that he was insane.
3. McMurphy's (Mac) behaviors do not seem to be symptoms of insanity. The case of Durham vs. United States held that "the accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect". Mac was trying to get out of the work farm by acting out and convincing the staff that he was insane. Once he was brought to the ward it was determined by the doctors and Nurse Ratched that he was not insane, but could be dangerous. In 1972 the Durham rule was replaced because of confusion in the courts about the definition of "disease". It was replaced by legal guidelines formulated by the American Law Institute and was combined with the M'Naughten principle.