In 1961, Stanley Milgram shocked the Psychology community by disproving the 'Germans Are Evil' hypothesis in the most ethically troubling study.
Outlined in this video are five factors which may influence the results of Milgram's study:
People are socially conditioned to conform and obey.
People accept instruction from an authority figure who they perceive to be more knowledgeable than themselves.
People will display attitudes and behaviours which support causes they believe in - even if they wouldn't condone the specific behaviour in another context.
People separate themselves from responsibility for their actions by assuming an 'agentic state'.
Volunteer Bias - Milgram's results might not be representative of the wider population because all of his participants volunteered to take part. Maybe the results are only reflective of a certain type of person.
Cognitive Dissonance - Not all of Milgram's participants committed 'murder', but all of them 'tortured' their learner. The participants who stopped short of murder may have experience cognitive dissonance, which led to their refusal to continue the experiment.
There are many ethical and methodological limitations of Milgram's initial obedience experiment (some of which have been addressed in follow up studies and reviews), but it is important to acknowledge that within the scenario created at Yale in 1961, 65% of participants would have committed murder if the shock generator had been plugged in.