Scott Alexander ponders what an outgroup really is in a long post: I Can Tolerate Anything Except The Outgroup.
It seems to me that you only pardon the sins that you don’t really think sinful. You only forgive criminals when they commit what you don’t regard as crimes, but rather as conventions. You forgive a conventional duel just as you forgive a conventional divorce. You forgive because there isn’t anything to be forgiven.
…But the best thing that could happen to this post is that it makes a lot of people, especially myself, figure out how to be more tolerant. Not in the “of course I’m tolerant, why shouldn’t I be?” sense of the Emperor in Part I. But in the sense of “being tolerant makes me see red, makes me sweat blood, but darn it I am going to be tolerant anyway.”