A military leader talking about teaching his daughter that their enemies were lowly and deserved being hated and hurt. The reason for the war might have sounded righteous in the ears of some: the people were poor and hungry and the war spoils gave them food. The prisoner of war commented "Her belly might be full, but her spirit will be empty," referring to the indoctrinated daughter.
This is a scene from Star Trek, but even if the series is science fiction, this fragment struck me as depicting a very real issue.
War is a matter of perspective. The side that you're on is in the right and the other one is wrong. Maybe from all points of view.
This is why the devil was created, so we could have an embodiment of evil to hate and fear. Likewise, many artful leaders have led their people to war against make-believe foes. See the crusades, Hitler's wars and possibly others.
It doesn't only happen in war either. We see it in everyday life. It's called discrimination. It's when we think one person or one group is bad just for a single trait we might not like or simply don't understand.
Sadly, these fallacies can cost lives and the happiness of many people. It only starts with one small misconception.