IMO and experience, it comes from the previous generation and is passed along UNTIL someone has the consciousness to STOP IT! I stopped it by not having kids and by going into therapy and 12 step groups. When I saw how family mental SICKNESS is passed along, it's easy to understand why and how there is so much brutality, horror and VIOLENCE in the world. If you get a chance, read a few books by Alice Miller [google her] in which she carefully describes why and how Hitler and his pals became such horrible monsters - thanks to the horrible way they were raised!
jim