We regularly ignore the fact that the thirst for vengeance is among the strongest of human emotions. It ranks with love, anger, grief, and fear, about which we talk incessantly. Modern state societies permit and encourage us to express our love, anger, grief, and fear, but not our thirst for vengeance. We grow up being taught that such feelings are primitive, something to be ashamed of and to transcend.
Jared Diamond [via Annals of Anthropology: Vengeance Is Ours: Reporting & Essays: The New Yorker]