"A king may move a man. A father may claim a son. But even if the men who move you be kings or men of great power, your soul is in your keeping alone. When you stand before God you cannot say, 'But I was told to do thus,' or that 'Virtue was not convenient at the time.' That will not suffice. Remember that."
--King Baldwin IV (Kingdom of Heaven)
Two negative forces work against seeking truth and doing the right thing. One stems from the axiomatic need to economize. Resources that advance standard of living are scarce. Material things are scarce, but so are intangible resources such as time an energy.
In order to get the most standard of living at the lowest cost of scarce resources, people are tempted to use aggression to satisfy their need to economize. Aggression enables people to take production from others, which allows the aggressors to economize their time and energies on other endeavors. Individuals might do the taking directly, or they might employ strong armed agents to do their bidding for them. Either way they are principals of violence and forcibly acting on others in order to get more for less.
The other force is bowing to social pressure. Because people accrue self esteem from group affiliation, they will bend their behavior to comply with group norms. Individuals are tempted to engage in activities for 'the greater good' or similar rationale. Social pressure to compromise one's morals and beliefs is often intense and difficult to sidestep.
Economizing via aggression and bowing to social pressure. Much evil in the world is driven by these negative two forces.