Now would be a good time to re-read Well-Kept Gardens Die By Pacifism in its entirety.

I did. It was about how community should allow moderator to make decisions the moderator considers necessary to protect the community.

It wasn't about how one faction should use external criticism to create a new rule to exile an opposing faction. That would be more similar to Evaporative Cooling of Group Beliefs.

A few years back, I was on a transhumanist mailing list where a small group espousing "social democratic transhumanism" vitriolically insulted every libertarian on the list. Most libertarians left the mailing list, most of the others gave up on posting. As a result, the remaining group shifted substantially to the left. Was this deliberate? Probably not, because I don't think the perpetrators knew that much psychology. (For that matter, I can't recall seeing the evaporative cooling analogy elsewhere, though that doesn't mean it hasn't been noted before.) At most, they might have thought to make themselves "bigger fish in a smaller pond".

This is one reason why it's important to be prejudiced in favor of tolerating dissent. Wait until substantially after it seems to you justified in ejecting a member from the group, before actually ejecting. If you get rid of the old outliers, the group position will shift, and someone else will become the oddball. If you eject them too, you're well on the way to becoming a Bose-Einstein condensate and, er, exploding.