This is a debate that has gone on for centuries. To understand this on going debate one must understand some basic terms. The first is punishment which Merriam-Webster defines as "a penalty inflicted on an offender through judicial procedure" (2006 Merriam-Webster, Incorporated), and the next is crime "an act or the commission of an act that is forbidden or the omission of a duty that is commanded by a public law and that makes the offender liable to punishment by that law; especially: a gross violation of law" (2006 Merriam-Webster, Incorporated) and finally recidivism "a tendency to relapse into a previous condition or mode of behavior; especially: relapse into criminal behavior" (2006 Merriam-Webster, Incorporated). There are many different views, but at the heart of the debate lies the question "Does punishment deter crime?" The goal is to find out the most effective way to prevent crime.
When a crime is committed now matter how severe almost everyone in society believes that the criminal should be punished.
From a sociological point of view one might ask why these criminals need to be punished. There are four different justifications for punishment which are retribution, deterrence, rehabilitation and societal protection. Which side of the debate one is on is usually determined by how each individual justifies punishment.
Retribution is defined as "something given or exacted in recompense" (2006 Merriam-Webster, Incorporated). This is basically "eye for an eye" justice and is the oldest form of justification for punishment. In principle retribution calls for the punishment to be as severe the crime committed. While this can be perceived as an equal punishment, opponents of this view argue it is just a small step above barbarianism, and it does not help to reform the criminal which can lead to recidivism.