Those people who become perpetrators of evil deeds and those who become perpetrators of heroic deeds are basically alike in being just ordinary, average people.
The banality of evil is matched by the banality of heroism. Both are not the consequence of dispositional tendencies, not special inner attributes of pathology or goodness residing within the human psyche or the human genome. Both emerge in particular situations at particular times when situational forces play a compelling role in moving individuals across the decisional line from inaction to action.
There is a decisive decisional moment when the individual is caught up in a vector of forces emanating from the behavioral context. Those forces combine to increase the probability of acting to harm others or acting to help others. That decision may not be consciously planned or taken mindfully, but impulsively driven by strong situational forces external to the person. Among those action vectors are group pressures and group identity, diffusion of responsibility, temporal focus on the immediate moment without entertaining costs and benefits in the future, among others.
The military police guards who abused prisoners at Abu Ghraib and the prison guards in my Stanford Prison experiment who abused their prisoners illustrate the "Lord of the Flies" temporary transition of ordinary individuals into perpetrators of evil. We set aside those whose evil behavior is enduring and extensive, such as tyrants like Idi Amin, Stalin and Hitler. Heroes of the moment are also contrasted with lifetime heroes.
The heroic action of Rosa Parks in a Southern bus, of Joe Darby in exposing the Abu Ghraib tortures, of NYC firefighters at the World Trade Center's disaster are acts of bravery at that time and place. The heroism of Mother Teresa, Nelson Mandela, and Gandhi is replete with valorous acts repeated over a lifetime. That chronic heroism is to acute heroism as valour is to bravery.
This view implies that any of us could as easily become heroes as perpetrators of evil depending on how we are impacted by situational forces. We then want to discover how to limit, constrain, and prevent those situational and systemic forces that propel some of us toward social pathology.
It is equally important for our society to foster the heroic imagination in our citizens by conveying the message that anyone is a hero-in-waiting who will be counted upon to do the right thing when the time comes to make the heroic decision to act to help or to act to prevent harm.