People are less willing to share information that contradicts their pre-existing political beliefs and attitudes, even if they believe the information to ...
its only group think in that a lot of the group independently think the same thing.
Groupthink is a psychological phenomenon that occurs within a group of people in which the desire for harmony or conformity in the group results in an irrational or dysfunctional decision-making outcome. Cohesiveness, or the desire for cohesiveness, in a group may produce a tendency among its members to agree at all costs. This causes the group to minimize conflict and reach a consensus decision without critical evaluation.
Emphasis mine
https://en.m.wikipedia.org/wiki/Groupthink