We have met the enemy and it is us. A controversial experiment demonstrates how easily evil that is in us all can be tapped by authority figures; even just a guy in a lab coat. It was controversial not just for its findings, but for the post-experiment effects and stress on participants administering the potentially fatal punishment. They discovered evil was their choice and couldn't be passed off as "following orders" when they were volunteers. They could have stopped at any time, but continued when persuaded but not forced by a perceived authority figure.
Obedience to authority experiment Stanley Milgram revisited.