Technology

Right, but that will also mean that the community will no longer be “big”. That’s my point.

My best counter-example is to look at (well... pre-Reddit-API-controversy...) r/ask_historians. It's one of the largest subreddits that became notorious for it's very strict moderation. If a big community is defined by either user-count or unique participating users (as a proxy to gauge how close-knit everyone is), I think it classifies as both easily.

Even after it became very tightly moderated, it's subscriber count generally tracked the growth rate of other subreddits. Even if the unique participant count growth rate is lower than other subs, I don't think it ever felt "close-knit".

If mods started going as far as deleting threads on the basis of “this discussion is already beaten to death and is not bringing anything new”, you can bet that this will be taken as an act of “censorship” and will cause everyone to leave to form their own factions

Participation in forums isn't (entirely) a zero-sum game. Groups of people can break off and still participate in the old space.

There's also no realistic way to handle users that default to not trusting moderators who are trying to make a good-faith attempt at community building. It's a cooperative exercise at any scale.

• except maybe the ones that are aligned with the mods enough to understand the principles behind the decision.

IMO this relationship between users and mods is the only one that matters. Assuming the mods are acting in good faith, this combination seems to be the only way to grow a community that won't implode on the first bout of controversy.