In the case of Terry Foucha v. Louisiana, the U.S. Supreme Court ruled in 1991 that a state cannot constitutionally continue to confine a mentally ill person who is not dangerous and whose sanity has been restored. The court held that such confinement violates an individual's substantive due process rights under the Fourteenth Amendment. Terry Foucha was found not guilty by reason of insanity for a small theft and illegal discharge of firearms, after which he was committed to mental institutions as per Louisiana law at that time. After four years, doctors concluded he had recovered from his drug-induced psychosis but diagnosed him with an antisocial personality disorder - this doesn't qualify as mental illness under state law; however, they couldn't certify him non-dangerous so he remained confined indefinitely without review or release procedures in place.

In the dissenting opinion for Terry Foucha v. Louisiana, Justice Clarence Thomas, joined by Chief Justice William Rehnquist and Justices Byron White and Antonin Scalia, argued that the majority's decision was inconsistent with previous rulings on civil commitment. They contended that dangerousness alone could justify a state's decision to continue confinement of an insanity acquittee who is still mentally ill. The dissenters believed that it was not irrational or arbitrary for Louisiana to conclude that Foucha posed a danger to society due to his antisocial personality which had manifested in violent behavior while institutionalized. They also pointed out inconsistencies in the majority’s reasoning regarding equal protection claims; they noted other instances where states can confine individuals based solely on their potential danger to others without violating constitutional rights (e.g., pretrial detention). In conclusion, they disagreed with the majority’s view about what constitutes punishment versus regulatory action by arguing there are legitimate reasons beyond retribution or deterrence for confining certain individuals.