Do you ever wonder how some people can believe what they believe when it is so different from what you believe? How is it possible? A primary reason this occurs rests on two principles of social psychology:
The First Principle: We consider our beliefs to be true to the extent that they are affirmed by a group of which we are a member. From the giant of social psychology Leon Festinger: “an opinion, a belief, an attitude is perceived as ‘correct,’ ‘valid,’ and ‘proper’ to the extent that it is anchored in a group of people with similar beliefs, opinions and attitudes.” Thus, “when a subjectively held belief is socially shared, it attains the status of objectivity.” Source.
The Second Principle:”Groups can only exist to the extent that their members have a shared understanding of the world.” Groups provide a sense of shared reality to their members. They provide us comfort as fellow group members support and reinforce our views of the world. Groups cannot exist if their views are too disparate. The more aligned/homogeneous group views are, the more entitativity or “groupiness” the group will have and the more they will be capable of fostering extreme views and beliefs. Source.
Groups and beliefs create a self-reinforcing loop. From the outside, you may view a group’s beliefs as ridiculous. Inside the group, the beliefs seem unassailable. This “groupthink” of beliefs and groups reinforcing each other can lead to extreme views not in line with reality.
For example, people who are not members of the Church of Scientology likely view Scientology beliefs as bonkers. However, for those inside the group, their beliefs ring true. Their beliefs are affirmed everyday by their fellow group members and their subjective beliefs in Xenu and the space opera is moved to the level of objective truth for those persons inside the Scientology group.
Stop and think about to what groups you belong. How have these groups moved mere belief to objective fact in your mind?
A related concept is that people are only fanatical about beliefs of their group which are not unassailable facts. It tends to be subjective beliefs reinforced by their group(s) that they hold most dear. Here’s philosopher and polymath Bertrand Russell on this point:
[T]he most certain kinds of knowledge are those about which there is least dispute . . . [but] these are not the kinds of knowledge, or supposed knowledge, that are asserted with most vehemence. Everyone is agreed about the multiplication table, but no one goes about proclaiming that it contains Sacred Truth. If anyone were to deny its truth, he would not be burnt at the stake or imprisoned as a fifth columnist. A sensible man, if he fell among arithmetical heretics, and were asked to recant his belief in the multiplication table, would do so, conscious that his recantation could do the multiplication table no harm. These are the characteristics of a belief about which there is no reasonable doubt.Russell, Bertrand. The Art of Philosophizing: And Other Essays
Thus, people tend to most hold dear subjective beliefs that are “true” primarily because their social group says such beliefs are true. Further, actual facts can be dismissed when they conflict with the beliefs held by the group.