It's a Job. A Monstrous Job.
Tell a person that something is his or her job and you may open a gate to a meadow or lock them in a narrow channel. Either way, they are likely to take the job seriously. [Granted, there are notable exceptions.]
While studying the Holocaust, I've often wondered about the extent to which so many people participated in the planning, construction, and operation of the death camps solely because it was their job. After all, those facilities had file clerks, secretaries, architects, builders, plumbers, engineers, electricians, lawyers, cooks, railway workers, and others who weren't involved in the bloodier part of the crime. A company supplied ink for the tattoos. Some architects designed the camp structures and lay-out. When you have a small part in the killing process, delusion and deniability are possible. You can tell yourself that your role is only a small part. If you are actually pushing people into gas chambers then your dodge is to say that you were following orders.
Much has been written about the Holocaust. A detailed analysis of the "indirect" participants is long overdue.
Who is more evil: the guard patrolling the perimeter or the architect who drew up the plans?