Maybe it is all due to conditioning. It is easy to achieve all you have to do is to install a belief system. Throw in some violence in movies and to top it off add some slow acting mind altering chemicals into the water and food supplies. Presto you now have created violence loving zombies that will enact on what they see and believe. What is the benefit? It keeps the zombies too busy and to dumb to see the reality of what is going on.