The central purposes of the death penalty, according to its proponents, are retribution, deterrence, and incapacitation.123 None justifies the execution of persons with mental retardation.
For the goal of retribution to be satisfied, an offender must "deserve" his punishment because he chose to commit a crime and knew what he was doing. As the U.S. Supreme Court has stated, "The heart of the retribution rationale is that a criminal sentence must be directly related to the personal culpability of the criminal offender."124 But since mental retardation precludes the high moral blameworthiness that is supposed to be a prerequisite of capital punishment, executing an offender with mental retardation cannot be justified as giving him his "just deserts."
Imposing the death penalty on persons with mental retardation is also not necessary to advance the putative goal of deterrence.125 People with that disability are generally unable to anticipate consequences of their actions and assess their options; there is no basis for believing their eligibility for the death penalty deters their commission of capital crimes. If offenders with mental retardation were excluded from capital punishment, other offenders would still be liable to the death penalty.
Finally, the death penalty is not the only means available to society to incapacitate people who pose a danger to society. Secure confinement of dangerous mentally retarded offenders adequately protects public safety.
123 See generally Edward Miller, "Executing Minors and the Mentally Retarded: The Retribution and Deterrence Rationales," 43 Rutgers Law Review 15 (1990).
124Tison v. Arizona, 481 U.S. 137, 149 (1987).
125 There is no empirical evidence that the existence of the death penalty has any deterrence effect; to the contrary, there is considerable evidence that it has no such effect. For example, as a recent New York Times analysis of state homicide rates revealed during the last 20 years, the homicide rate in states with the death penalty has been 48 percent to 101 percent higher than in states without the death penalty. See, Raymond Bonner and Ford Fessenden, "Absence of Executions: A Special Report," New York Times, September 22, 2000. See also, Jon Sorensen, et al., "Capital punishment and Deterrence: Examining the Effect of Executions on Murder in Texas," Crime and Delinquency, (October, 1999), pp. 481-493.