Punishment and the Principle of Equality
The principle of equality, that great tradition of Anglo-American civilization, applies itself in the criminal law not only in a defendant's defense but also in his prosecution and punishment. The Equal Protection Clause of the Fourteenth Amendment to the Constitution proscribes equal protection under the law to every citizen of the United States. It's in this very spirit that a certain amount of equality is proscribed in the prosecution of like crimes, even when individual justice and common sense might suggest otherwise. A simple example may illustrate this point.
A man and his wife are walking down an empty street at night, when suddenly they're accosted by some roguish fellow with a long history of violent crime (let's call him Barney) and asked to relinquish their wallets. Barney is not armed, but he's fairly large, and intimidating enough without a weapon. When the couple hesitates, Barney moves as if to attack. The huband, who watches a lot of action movies, grabs his pocketknife and without thinking jabs it into Barney's neck, puncturing Barney's windpipe and causing him drown to death in his own blood.
What sort of punishment does the husband deserve? At trial, a hypothetical court determines that, although the husband was acting in self defense, his use of force was excessive. Although the court determines the husband's act satisfies the "adequate provocation" requirement that avoids a potential murder charge, he is found guilty of voluntary manslaughter, a serious felony that usually carries an active prison term. But what if the husband is a respected member of his community, with no criminal record, a valued employee, husband, father, and friend to many? Barney, the man he killed, was an inveterate criminal who'd hurt and robbed many people before and probably would have continued doing so if his life hadn't come to such a swift and unexpected end. Does the husband deserve to be punished at all?
Society probably doesn't need any protection from this man, so he probably doesn't need to be restrained or removed from society - in fact, since he is the primary bread-winner of the household, imprisoning him could be very detramental to his family. Nor would it seem that he needs time in prison to deter him from committing further crimes. There seems to be little retributive value to a prison term, since it's questionable how much injury he really inflicted on society (it might even be argued he improved society a little) and, while there might be some general deterrence value against others using excessive force, there is no need at all to rehabilitate this man into a productive member of society. In fact, a prison term runs the risk of releasing a man who is significantly worse than the one man who first entered.
Still, the principle of equality that rests at the heart of our society requires that felons be treated with some degree of equality, no matter what the individual circumstances. Although this can conflict with individual justice, it is a fundamental priciple of our civilization. Voluntary manslaughter is a very serious felony and, no matter how sympathetic individual circumstances may be, the principle of equality in "a nation of laws" like the United States is not commensurate with the very same crime being punishable for some and excusable for others. In our hypothetical case, as in countless real life cases, the defendant will face a substantial prison term - perhaps three to five years in prison- "on principle."
[A happy afternote: In real life, it's not unheard of for a judge to forgo a prison sentence in exceptionally sympathetic cases like the one above. According to modern theories of compensatory punishment, all of our hypothetical defendant's obligations to society might be fulfilled by a lengthy probation, along with significant community service. Not only might this sentence satisfy his debt to society, it would prevent his family from being torn apart.]