Jeffrey Dahlmer raped, killed and ate parts of at least thirteen men. As punishment, the government was planning to feed, clothe, educate, medicate, entertain, and legally represent him for the rest of his life. Families of his victims would pay taxes, in part, to keep Dahlmer comfortable, warm in winter and cool in summer. That type of punishment should scare the dickens out of other mass murderers. Interrupting the governments plans for Dahlmer however, an inmate beat the cannibal to death in prison.
Some oppose the death penalty on practical grounds, arguing that it is not a deterrent. However, in the late sixties, when there were an average of 6,000 murders a year, the United States Supreme Court struck down the death penalty as unconstitutional in the way it was administered. Six years later, when it was re-instituted in the early seventies the number of average annual murders had jumped to nearly 16,000 victims per year.
In countries like Saudi Arabia, which enforce a swift and certain death penalty, violent crime is rare. Singapore and Los Angeles have equivalent populations, yet in one year Singapore had 58 murders (most followed by swift execution) while Los Angeles had 1,063. Criminal sub-cultures like the Mafia show that the death penalty is a powerful deterrent even among career criminals, since few will ever double-cross their superiors, fearing the repercussions.
Others oppose the death penalty on moral grounds. The "morality" arguments of atheists are not persuasive because if there is no God, then there is no absolute morality, only arbitrary and subjective opinion. The anti-death-penalty morality arguments of some Christians, on the other hand, are persuasive to many. They base their arguments on statements made by Jesus Christ and therefore many listen attentively.
These "moral" opponents of the death penalty often intimidate good people into shying away from execution. Many Christians claim society should forgive criminals and instruct them to "go and sin no more." Ideas have consequences and the popularity of this idea parallels a huge sustained crime epidemic.
There is a right way to deter criminals and to end the crime epidemic. That deterrence, however, does not lie in telling Dahlmer to "go and eat no more."