When members of a cult don’t trust outsiders, it allows their beliefs to drift away from reality. They’re not getting the feedback necessary to keep information grounded. And reality is a great mechanism for keeping beliefs unified. The creation of cults has splintered the USA.
I think the Internet has helped foster this. It made it cheaper and easier to create a new news source. It is cheaper and easier to fund that news source through ads or direct payments from customers. And the resulting market incentivizes news sources to keep customers by denigrating the competition, which creates cults.
We need to redesign the market for news sources, to disincentivize that behavior.