Suppress and conquer. How do people lose their humanity?

If you order a person to shock another for incorrect answers, then he will follow the order until he kills. If you offer a person to become a guard in a prison where his classmates are kept, then on the first day he will do everything possible to avoid the need to show cruelty, but only on the first day, and then the experiment will have to be stopped due to cases of uncontrolled aggression on the...