Still, if they try to define what a cult is (even if they do that later, after the conversation), that alone can help them answer their underlying questions.
as being so much about rationality as it is about our relationship with dissonance
It seems to me that most of rationality is about our relationship with dissonance. Though in most cases that dissonance is implicit while here it is obvious.
But you should have put that silly hat on!
It's like in programming, objects pointing to different versions of the same parent object—because our subconscious software cloned the parent object and not referred to a single copy of it. And now we have some unreviewed code and "belief leaks" (by the analogy with memory leaks).
And some emergent properties for sure!
Another problem with some people is that they don’t consciously believe (or won’t openly admit) they have absolute certainty. In their speech, they say that they doubt this and that, that they "cannot know everything" but I guess that’s mostly a trick for them to say "and neither do you." With them, one first needs to convince them that they are lying to themselves before having a talk about certainty vs uncertainty.
It reminds me of how rich dialogue choices always constitute a part of great RPGs. You cannot pretend to have done good work on a role-playing game if dialogue options boil down to "Tell me more", "Yes", and "Not now".
I’m instantly thinking about politics: there are many cases where you cannot build a clear model of what’s going on exactly in a given government, and the information is not only not transparent but also degraded with all the noise, intentional and not. I think it’s reasonable to maintain the feeling of doubt while ruminating on such topics.