The history of the world has demonstrated that groups with negligible differences can hate each other and cause death and misery.  This is a result of our evolved tendency to positively evaluate those who belong to the same groups as us and negatively value people outside our groups.  Unfortunately, this evolved trait works even when the groups are clearly arbitrary.  This allows us to be rabid sports fans but also vengeful political partisans.  Also, the Chicago Bears and their fans are despicable unholy creatures.  #FIBs