Why do you think that societies have not discussed forgiveness in an open and large-group way? I have never seen a discussion of this as I have, for example, about such important issues as the death penalty, abortion, and other issues that have direct implications for the overall quality of life.
I, too, am puzzled by the silence over centuries regarding a thoroughgoing discussion of forgiveness in any society in the world. Has it just been off the radar of leaders? Have the burdens of justice and injustice been so large that mercy has been left by the side of the road? It could be that leaders historically have considered forgiveness to be part of religion and so have compartmentalized it there. Now that forgiveness has made its way into philosophy, psychology, law, medicine, and education, it seems to me that it is time for leaders to encourage a discussion of forgiveness in families, in schools, and between groups and countries that experience conflict. The world would be a better place with forgiveness growing up alongside justice in many communities, societies, and countries.