Religion fanatism, Nationalism, Racism you name them as long as it is dividing people, or making some of them think they are better than the others, ie black or white, Muslim or Christian, Israeli or Arab, If you have individuals like these, like you said it is easy to influence them, and you can use books or leaders as tools and control them the way you want, isn't it to do with stupidity? that you let others to control you, instead of choosing your life the way you want, and not live for others?