In the 1988 case of Penry v. Lynaugh, Johnny Paul Penry was convicted for murder in Texas and sentenced to death. His lawyers appealed on the grounds that he had intellectual disabilities, arguing that executing him would violate his Eighth Amendment rights against cruel and unusual punishment. The Supreme Court ruled 5-4 against Penry, stating that while it is constitutionally permissible to consider mental disability as a mitigating factor in sentencing, it does not categorically exempt someone from capital punishment. However, this decision sparked significant controversy over whether individuals with intellectual disabilities should be eligible for the death penalty at all - an issue which was later addressed by Atkins v. Virginia (2002), where such executions were deemed unconstitutional.

In the dissenting opinion for Penry v. Lynaugh, Justice Brennan, joined by Justices Marshall and Blackmun, argued that executing mentally disabled individuals constitutes cruel and unusual punishment in violation of the Eighth Amendment. They contended that such persons have less culpability due to their diminished capacities for understanding consequences or controlling impulses. The dissenters also pointed out that these individuals are more susceptible to wrongful conviction because they may be easily led or manipulated during interrogation processes and might not fully comprehend legal proceedings against them. Furthermore, they asserted that executing mentally disabled people does not serve any legitimate penological purpose as it neither deters others nor retributively punishes the offender who lacks full comprehension of his actions' gravity.