The pardon power is a genuinely important Constitutional power; it is one of the means whereby government is restricted in favor of what is good for the people. Why do we need the pardon power? As I said once before,
[B]ecause sometimes, as James Wilson puts it, people "may be unfortunate in a higher degree, than that, in which they are criminal." And because sometimes, due to particular circumstances of the case, we can make a reasonable judgment that we would all benefit more if the person involved were given a second chance. And sometimes, perhaps just a little, because we need some clear symbol that laws are not perfect, that courts are not flawless, that mistakes are not unforgivable, and that compassion is essential to the health of justice.
The quotation from Wilson, one of our Founding Fathers, is from his lectures on law:
Citizens, even condemned citizens, may be unfortunate in a higher degree, than that, in which they are criminal. When the cry of the nation rises in their favour; when the judges themselves, descending from their seats, and laying aside the formidable sword of justice, come to supplicate in behalf of the person, whom they have been obliged to condemn; in such a situation, clemency is a virtue; it becomes a duty.
As Alexander Hamilton noted,
Humanity and good policy conspire to dictate, that the benign prerogative of pardoning should be as little as possible fettered or embarrassed. The criminal code of every country partakes so much of necessary severity, that without an easy access to exceptions in favor of unfortunate guilt, justice would wear a countenance too sanguinary and cruel.
There is, I think, a disturbing tendency to deprecate the pardon power as too soft. This is a sign of a way in which we are less than our Founders: less civilized and more barbaric.