Well the conclusion itself is rather simple to understand. The origin of such behavior is rather vague, but I could probably form a theory. Right from the start, the reason in which most people develop such beliefs and behaviors within their lives revolves around socialization and normality. To some extent, all people possess a tendency to conform, and many will even conform to the point of inauthenticity. Abnormal behaviors are typically condemned partially in concern for the individual's safety but also in concern for the well being of society. Tradition is oftentimes seen as a tested formula for success, and it minimizes the potential for risk. At the same time, without that potential for change, neither the individual nor the civilization may improve and progress either.

Still, this can be somewhat of a pendulum. While progression is a necessary tool for evolution, many people place so much emphasis upon the concept of progress that their actions reflect something quite regressive in nature. When a group attempts to force a narrative or agenda in the name of progress, it usually comes with its own share of victims. This creates a division between people of various ideologies, and the potential for negotiation quickly diminishes. Even though much of humanity has come quite a long way in its moral compass, it is not immune to regressing back into its previous states. Civilizations have a tendency to progress and regress in the face of heightened political, religious, or philosophical turmoil. The problem is, people usually assume that it is the "opposite" side which is causing such regression when in reality, it may oftentimes be their own side or even both sides (perhaps even multiple conflicting ideologies). When understanding progress, one must not only account for who it assists, but they must also account for who it harms. If there must be innocent victims in the name of such progress, then I doubt it really qualifies as progress.

It is not quite true to say that people are simply "good" or "evil" either. While one is still responsible for their own actions and behaviors, many individuals are simply never exposed to any other ideologies other than those in which they were raised under. Even today, at the peak of technology, people are often uncomfortable with overstepping that boundary into the ideas which contradict their own beliefs. And it is not a single group -- it affects practically everyone to some extent or another. To overstep that boundary is a conscious effort on one's own behalf, and to overstep it frequently is a habit which must be developed in time.