The deterrent theory by showing that crime never pays separate the motive., while the reformative theory seems to strengthen the character of the man so that he may not become victim of his own temptation. This theory would consider punishment to be curative or to perform the function of medicine.
According to this theory crime is like a disease. . This theory maintains that you can cure by killing.
The ultimate aim of reformists is to try to bring about a change in the personality and character of the offender, so as to make him a useful member of society.
Today, on the other hand, this theory is based on the idea that punishment is the necessary alkali to neutralize the evil effects of crime. The idea behind the retributive punishment is that of the restoration of the moral character, the appraisement of the disturbed conscience of society itself and the maintenance of the sovereign power of the state which becomes aggrieved when a crime is committed and inflicts punishment to set matters of right. Though the system of private revenge has been suppressed, the instincts and emotion that lay at the root of these feelings are yet present in human nature. Therefore, according to this moral satisfaction that the society obtains from punishment can not be ignored.
On the other hand, if the criminal is treated very leniently or even in the midst of luxury, as the reformative theory would have it, the spirit of vengeance would not be satisfied and it might find its way through private vengeance. According to this theory eye for eye and tooth for tooth is deemed to be a complete and really sufficient rule of natural justice.
In the last, we can easily say that the only logical inference from the reformative theory, if taken itself, is that they should be abandoned in despairs as no fit subject for penal discipline. The deterrent and disabling theories on the other hand, regard such offenders as being pre-eminently those with whom the criminal law is called upon to deal.
The application of purely reformative theory, therefore would lead to astonishing and inadmissible results. The perfect idea of criminal justice is based on neither reformative nor the deterrent principle exclusively, but the result of comprise between them.
In this it is the deterrent principal which possesses predominant influence. It will not be out of place to mention here that Gandhi ji "hate the sin and not the sinner", is merely a philosophical assertion and can not furnish a practical guide in the administration of justice.