In reading some sermons by Martin Luther I came upon a concept I hadn't considered before.
Luther draws a distinction between the duties of the Christian as an individual and the duties of the Christian (or non-Christian) as a civil authority.
The distinction is that the Christian as an individual should always forgive and the civil authority should never forgive, but only exercise justice.
Not forgive? But that's at the very heart of Christianity!
But Luther points to Romans 13, which says the civil authority "does not bear the sword for nothing." And he also refers to Jesus distinction between two realms, the realm of civil authority and the realm of God's authority ("Give to Caesar what is Caesar's and to God what is God's" - Matt 22:21).
The civil authority's task, Luther says, is to punish criminals to maintain order and justice (not, by the way, to impose Caesar's authority on God's realm or vice versa). In the pursuit of that job the magistrate is to punish, not to forgive. In fact, the "sword" reference in Matthew 22 suggests that the civil authorities may also make use of the death penalty.
I find Luther's arguments mostly persuasive. Forgiveness, it seems, is only valid between the injured party and the injurer. So, if Joe hurts Sam, Sam can forgive Joe, while Robert, who is uninvolved, cannot forgive Joe for an injury to Sam.
But a judge is supposed to be an uninvolved person, a "Robert." Therefore, while a judge (for example) can take all extenuating circumstances into consideration - such as a killer being severely provoked, for example, or that the injury is absurdly small (your walking on someone else's grass) - and can properly adjust any judgment accordingly, the judge can't just forgive criminal behavior. Forgiveness is the task of the injured party alone; enforcing justice is the task of the civil authorities, even if those in authority are Christians.