People by nature desire unity and are abhorred by disunity however often what happens is people get abused, now we have a principle sinah mikakeles es hashurah hatred screws up the natural order of humanity, so now revenge, stepping on someone else to feel better about themselves (Arabs, Nazis, anstisemites, for example, all trying to step on Jews to feel better about their personal loss of prestige, for your brain perceives the outside world as your enemy hence anybody even your friend, the people who love and will help you will also do for this purpose,) so revenge distorts the natural drive for unity and people are willing to cause chaos, murder etc. just to feel better about themselves.