1. Incapacitation: A felon in prison cannot commit crimes while imprisoned. An executed felon cannot commit a crime ever again.2. Deterrence: The threat of punishment deters people from engaging in illegal acts.
3. Restitution: The felon is required to take some action to at least partially return the victim to the status quo ante.
4. Retribution: The felon harmed society; therefore society (or the direct victims) is entitled to inflict harm in return.
5. Rehabilitation: The punishment changes the felon in order to make him a better citizen afterwards. (The punishment can include mandatory vocational training, counseling, drug treatment, etc.)
In order for a punishment to be justified, it must satisfy at least one of these criteria. (There may be reasons to oppose a punishment even if it does satisfy these criteria, so this is a necessary, but not a sufficient, condition.)
Capital punishment clearly satisfies incapacitation. But so does life imprisonment without parole. Granted, there is a tiny, non-zero probability that the felon may escape and kill again (or kill a guard or another inmate). I think the difference is negligible (at least in the US, although in a place like Columbia or Peru that wouldn't be true), and most people treat the two as equally incapacitating. I'm not aware of anybody in recent history escaping from life without parole. There is clearly no possibility of restitution or rehabilitation if the felon is executed. So the decision on whether to alllow capital punishment hinges on retribution and deterrence.
The evidence raises serious questions about whether capital punishment deters more than life imprisonment. Violent criminals tend to have anger-control issues or be risk-seeking, harboring a belief that they won't be caught. If a potential felon believed he'd be captured, convicted, and incarcerated for life, how likely is he to commit the crime, and how less likely is he to do so if he believed he'd be captured, convicted, and put to death? Most just don't think they'll be caught. Many already risk death in confrontations with their victims or with police during capture, or in handling deadly explosives (in McVeigh's case). From an intuitive analysis, it just doesn't seem likely that capital punishment should deter much, compared to life without parole. Also, about 16,000 murders are committed annually in the US, while 98 people were executed in 1999. The likelihood of capital punishment appears to be very low, which would make one queston its deterrent effect.
A number of studies have tried to determine whether capital punishment deters murder. Some states have capital punishment, and some don't. And all the states that have capital punishment now did not have capital punishment in the late 1970s and reinstated capital punishment sometime in the 1980s or 1990s. The studies of deterrence are based on panel data--cross-sectional time series across states, trying to see whether capital punishment, when other factors are controlled for, deters murder. And, let me tell you, there is no convincing evidence that it deters crime. At best, it might deter a little bit. We'd be much better off deterring murder by taking the resources spent on capital punishment trials and investing in more crime-prevention programs.
Absent any conclusive evidence that capital punishment deters murder, (and if it does deter, it's only by a tiny bit), that leaves retribution as the real issue. In order to justify capital punishment, we have to accept that retribution is a legitimate objective of the criminal justice system. I am troubled by that. Retribution is used to justify "an eye for an eye." Retribution is based more on emotion than on rational policymaking. And, let's say for sake of argument that retribution is legitimate. Isn't life without parole retribution? In endorsing capital punishment based on retribution, one is really saying that the marginal gain in retribution value from execution compared to life without parole is what justifies the policy. There is still a whole lot of retribution embodied in life without parole.
Now let's bring in risk analysis. If a criminal is falsely convicted, life without parole allows that the falsely convicted may at some future point be freed. Years of imprisonment are wrongly imposed on the falsely convicted person, but this harm is less than the harm incurred by erroneously killing him. And, from the number of convictions recently overturned (or posthumously exonerated), it appears that this risk is orders of magnitude greater than the risk that someone given life without parole will ever kill again.
I would argue that, given the risk of false conviction, (and we have clear evidence that this has happened an alarming number of times) we should not accept capital punishment on the possibility that it may deter crime. We should want incontrovertible evidence that it deters before accepting that it has satisfied the deterrence criterion.
So, there you have it. In order to justify capital punishment, you must accept the following:
1. That retribution is a valid part of meting out punishment;2. That the increment in retribution value of execution versus life without parole is important;
3. That the increment in retribution is worth the added cost of trying capital punishment cases (compared to life without parole);
4. That the increment in retribution is worth the clear risk of false executions;
5. That the increment in retribution is worth all the moral arguments that people make against such a severe punishment (none of which have I discussed here).
I think that it is very hard to justify capital punishment. I think that those who do find it justified are really basing their justification on a very intense emotional sense of retribution.
