As your question implies, you are aware that there is more than one reason why forgiveness is good. To meet your challenge, I would say that the major reason why forgiveness is good is because it is linked to love, particularly what we call service love or agape love. When you forgive you are exercising this kind of love toward someone who has not been loving to you as seen in his or her unjust actions. Thus, forgiveness is good because it meets injustice with the heroic virtue of love. I call it heroic because it is so difficult to offer agape love in the face of others’ injustice.