(I'm neither a theology scholar nor an anthropologist, so I may lack some important background on this.)
I agree that the idea of early church leaders isolating members in order to explicitly limit the introduction of new ideas sounds far-fetched. It strikes me as the kind of thing that would only be said after the fact, by a historian looking for meaning in the details. But attributing those member-isolating rules to something like "preserving group identity" seems like the same thing.
I find myself wondering if something like the anthropic principle is at work here, i.e. the only religious groups to survive that long are the ones who historically isolated their members from outside ideas. There's probably a more general term for what I'm getting at.
There's probably a more general term for what I'm getting at.
Survivorship bias?
To break up the awkward silence at the start of a recent Overcoming Bias meetup, I asked everyone present to tell their rationalist origin story - a key event or fact that played a role in their first beginning to aspire to rationality. This worked surprisingly well (and I would recommend it for future meetups).
I think I've already told enough of my own origin story on Overcoming Bias: how I was digging in my parents' yard as a kid and found a tarnished silver amulet inscribed with Bayes's Theorem, and how I wore it to bed that night and dreamed of a woman in white, holding an ancient leather-bound book called Judgment Under Uncertainty: Heuristics and Biases (eds. D. Kahneman, P. Slovic, and A. Tversky, 1982)... but there's no need to go into that again.
So, seriously... how did you originally go down that road?
Added: For some odd reason, many of the commenters here seem to have had a single experience in common - namely, at some point, encountering Overcoming Bias... But I'm especially interested in what it takes to get the transition started - crossing the first divide. This would be very valuable knowledge if it can be generalized. If that did happen at OB, please try to specify what was the crucial "Aha!" insight (down to the specific post if possible).