No question in criminal justice raises the stakes as high as the death penalty, because it is the one punishment that cannot be undone. Thoughtful people have defended it and opposed it for centuries. This level presents the strongest case on each side, then the facts about wrongful convictions and international trends.

The case for

Defenders of capital punishment make several arguments.

• Desert. For the most terrible crimes, such as deliberate mass murder, only death is proportionate to the wrong. Kant held this view, and so, more surprisingly, did John Stuart Mill. In an 1868 speech in Parliament, Mill opposed abolition for the worst murders, arguing that a swift death was less cruel than a lifetime of hard labor and that it expressed society's judgment of the crime.
• Justice for victims. Some families of murder victims feel that anything less fails to honor the life taken.
• Deterrence and protection. Some argue the threat of death may deter some killers and that execution ensures a murderer can never kill again, including in prison.
• Democratic choice. Where most citizens support it, defenders say, it reflects the community's settled moral judgment.

The case against

Opponents answer with arguments of their own.

• Irreversibility and error. Every justice system makes mistakes. Prison sentences can be ended and partly compensated, but an execution cannot be undone.
• Unequal application. Studies in some countries have found that factors such as the quality of defense lawyers, the place of trial and the race of the victim affect who is sentenced to death.
• Doubtful deterrence. In 2012 a US National Research Council committee concluded that existing studies did not provide useful evidence on whether the death penalty increases, decreases or has no effect on homicide rates.
• Human dignity. Many argue that a state killing a defenseless prisoner violates the dignity it should protect, and that the right to life does not depend on good conduct.

Wrongful convictions

Wrongful convictions are not hypothetical. Since DNA testing entered criminal cases in the late 1980s, it has exonerated many people convicted of serious crimes, some of them sentenced to death. In the United States, for example, by the mid-2020s close to 200 people sentenced to death since 1973 had later been exonerated, by the count of the Death Penalty Information Center, though not all of these cases turned on DNA. Defenders of capital punishment reply that safeguards can be strengthened, and that the penalty could be limited to cases where guilt is beyond any real doubt, such as those with strong forensic evidence. Opponents answer that no system can guarantee certainty, and that confident cases have also turned out wrong.

International trends

The trend over the past century has been toward abolition. According to Amnesty International, as of the mid-2020s more than two-thirds of the world's countries have abolished the death penalty in law or in practice. The Second Optional Protocol to the International Covenant on Civil and Political Rights, adopted in 1989, commits its parties to abolition. Protocol 13 to the European Convention on Human Rights (2002) abolishes it in all circumstances, and abolition is effectively a requirement for joining the European Union. Since 2007 the UN General Assembly has repeatedly called for a moratorium on executions. At the same time, a number of countries, including some large ones, retain and use the death penalty, and most recorded executions take place in a small number of countries.

Thinking it through

The disagreement turns on a few questions: whether some crimes deserve death, how much risk of error is tolerable, whether the state should hold the power to kill, and what justice owes to victims. People of good will answer them differently.

Worked example: a debate in an invented parliament

The country of Arvenna has abolished the death penalty for ordinary crimes but kept it, unused for decades, for treason and mass murder. After a terrorist bombing kills forty people, a legislator proposes executing the captured bomber. Two members respond.

Member Rana speaks in favor. “Some acts are so monstrous that any lesser penalty tells the families of the forty that their loved ones' lives weighed less than the killer's. The evidence here is overwhelming: he was caught at the scene, filmed, and has confessed. If we keep this penalty anywhere, it is for cases like this. And he can never again direct attacks from a prison cell.”

Member Tomas speaks against. “I share the horror. But we cannot write a law for one man. The next case will be less clear, and courts in many countries have executed people later shown to be innocent. The research does not show that executions deter killers, least of all those ready to die for a cause, who may see execution as martyrdom. A life sentence protects the public, and it keeps the state out of the business of killing people who are already helpless.”

Notice how each speaker uses the arguments from this level. Rana relies on desert, certainty of guilt in this case, and incapacitation. Tomas relies on the risk of error in future cases, the doubtful deterrence evidence and human dignity. A listener deciding between them must judge which considerations weigh most, and whether a rule built for the clearest case can stay limited to such cases.