"Methodical" is the key word. Couple that with "obey or die", plus a good dose of "everyone is doing it", and most people will do anything, with little remorse, just to do their job, collect a paycheck, and go home at the end of the day.
Evil behavior can be surprisingly mundane. When made methodical and commonplace, few people would _not_ do it.
Hence the axiom that humans are inherently evil - very little encouragement is needed for most people to cross the line.
I don't think we are inherently evil per se, just easy to tip one way or the other (precariously balanced?). As we grow, we develop more conviction, furthering us away from that edge, in one direction or the other. The truly evil probably develop in that direction. The sheep that follow remain near the edge, forever easy to manipulate.