Rules, Biochemistry and Perception. Rules defines what's good or bad. Biochemistry is obvious. And perception, a fat finger pointed at things we see as "evil", through the limits of our personal imagination.
Education is a major factor in how a child grows. Not just the school, even at home and the surrounding environment, if the child is thought to live self reliance, and if he/she sees people manipulating others or dominating them by status, ofcourse he/she would come to conclusion that this the way to greatness. It isn't the lofty desire that is wrong, it's the path that's been shown. Many think we have to reach our goal no matter the cost. That's how they learn to step over others and push them of their paths. And truthfully, in our society if you are "soft-hearted" ( incapable of using others weakness to your strength) then you simply fall under the category of sheeps to be reared by the "Shepards". "evil is the pain of the majority, good is the service of others, but delusion is poison to all". practically no one can be called truly evil or truly good, even the most heinous terrorists have somehow helped people around them, even the most peace loving people have hurt others knowingly or unknowingly. All of us just want to live to ourselves, at times to make a choice the majority choose the one with least amount of risk to themselves and others. Too bright and you might burn yourself; Too dark and you blind yourself. Head or tails, you find yourself fail, Be the edge, so you can cut through the veil.
Root of evil definitely knowledge. They say knowledge is power I say it's evil but than again it depends on how you use your knowledge. Some people would use it for evil while some for good. Mostly human greed. People are simply never satisfied, they just keep wanting more. The more you have the more you need. Does that make sense?