Studies on obedience (e.g. replications of Milgrim Experiment) suggest a lot of factors play into people harming and killing others on behalf of an authority. Original was 65% of participants, but it can to up to 90% with men in authoritarian cultures.

My favorite was Australian women having the lowest rate of obedience in the shock experiment, at only 16%, being relatively individualistic and rebellious culturally, but even less obedient then men as women are less likely to conform when it involves harming others. That may have changed in recent years though, as people more comfortable with authoritarianism tend to be more likely to obey.

Typically, people least likely to obey the order have better social intelligence and moral development. Unfortunately, those traits are far and few between lately...