Arguments for and Against the Death Penalty from http://deathpenaltyinfo.msu.edu/

ARGUMENT 1
DETERRENCE
The death penalty prevents future murders.
Society has always used punishment to discourage would-be criminals from unlawful action.
Since society has the highest interest in preventing murder, it should use the strongest punishment available to deter murder, and that is the death penalty. If murderers are sentenced to death and executed, potential murderers will think twice before killing for fear of losing their own life.
For years, criminologists analyzed murder rates to see if they fluctuated with the likelihood of convicted murderers being executed, but the results were inconclusive. Then in 1973 Isaac
Ehrlich employed a new kind of analysis which produced results showing that for every inmate who was executed, 7 lives were spared because others were deterred from committing murder.
Similar results have been produced by disciples of Ehrlich in follow-up studies.
Moreover, even if some studies regarding deterrence are inconclusive, that is only because the death penalty is rarely used and takes years before an execution is actually carried out.
Punishments which are swift and sure are the best deterrent. The fact that some states or countries which do not use the death penalty have lower murder rates than jurisdictions which do is not evidence of the failure of deterrence. States with high murder rates would have even higher rates if they did not use the death penalty.
Ernest van den Haag, a Professor of Jurisprudence at Fordham University who has studied the question of deterrence closely, wrote: "Even though statistical demonstrations are not conclusive, and perhaps cannot be, capital punishment is likely to deter more than other punishments because people fear death more than anything else. They fear most death deliberately