Your post in turn reminds me of this lecture about situational contributors to violent and aggressive behavior. At 47:40 the lecturer discusses what he calls the "Lord of the Flies Effect".

He refers to a psychological study about the impact of anonymity on violent behavior. More interestingly, in my opinion, he mentions an anthropological literature review in which 12.5% of primitive societies that do not ritualistically alter their appearance (with face paint or masks) before battle are found to kill, mutilate, and torture their captives while 80% of those that do alter their appearance do so.