Ex-cultist here. Specifically, fundamentalist Christian in the US.

So what we're seeing here is a division between in-groups and out-groups, and drawing that circle closer as a means of guarding against valid criticism. Consider; the standard response of most cults when they are under attack is to double down on its assertions that it is telling the truth. Most cults are built with a persecution complex as key part of exploiting their believers.

This tactic triggers their emotional response to rally to the defense of their cause, because "We're under attack! We're being hunted! The Worst Thing Possible is going to happen, and it is THIS PERSECUTOR'S fault!" This also forces a false choice in members who are doubting the leadership, forcing them to either cut all social ties and side with the enemy (they are trained to see this as a fate worse than death) or rehearse their dogma and rally without question.