Ordinary people, simply doing their jobs, and without any particular hostility on their part, can become agents in a terrible destructive process. Moreover, even when the destructive effects of their work become patently clear, and they are asked to carry out actions incompatible with fundamental standards of morality, relatively few people have the resources needed to resist authority.
Control the manner in which a man interprets his world, and you have gone a long way toward controlling his behavior. That is why ideology, an attempt to interpret the condition of man, is always a prominent feature of revolutions, wars, and other circumstances in which individuals are called upon to perform extraordinary action.