While personal and selfish motives explain evil at an individual level, there is another facet to evil - 'Mass Hysteria' & 'Mob Mentality'. History of mankind is smeared with blood from evil perpetrated by indoctrinated mobs justifying those acts of violence as a service to their Gods, scriptures, culture or ideology.

Witch-hunts, holy wars, riots, etc. are all examples of this type of evil by common people leading a normal life, provoked by a call from their leaders who are often guilty of misguiding these mobs.

The root cause of this type of evil can be traced back to unfettered faith in some leader / ideology and indoctrination. Can people in general resist indoctrination? Because once our belief system is breached we can be manipulated into doing anything and there will always be those clever charismatic crooks waiting for an opportunity to cash in on such sentiments. It all boils down to what we accept as truth and how we make sense of our world with all its idiosyncrasies.

In the end, history repeats itself but we can change that if we learn to resist dogmas, value criticism, respect rational argument and realize that no belief is worth the blood and lives of our fellow men.