This is particularly true if membership in that group is based on shared thinking, such as the sort of church where you must all recite the same creed, the faculty of a school where there are written or unwritten expectations for what you will teach or publish, or a political party whose “platform” you must support.
The reason is obvious, isn’t it? As Alan Jacobs says in his book, How to Think,
…the pressures imposed on us by Inner Rings [of people who control such groups] make genuine thinking almost impossible by making belonging contingent on conformity.
He continues with the solution: