> Why is strong moderation part of a healthy online community
Membership criterion is central to maintaining the competency level of the members. And competency on the topic (along with intellectual honesty) is the single most, perhaps only, important component to a useful discussion: It would be insanely destructive for the New England Journal of Medicine to publish every single thing it ever received with equal weight in massive weekly tomes.
Moderation acts as competency monitoring to a degree.
The problem with literal membership is that it precludes autodidacts, people new to the field and people who can't be bothered with a complicated process for joining. Thus unrestricted membership with moderation. And indeed on reddit, the highest quality subreddit, /r/science, is the one most aggressively moderated
For fact based, purpose driven venues, if you believe you were censored because of your opinion, you should not have posted an opinion in the first place. That's certainly how it works in the workplace which is how some people need to use the web.
There can be unlimited venues where partially informed people post their opinions, maybe we can call them "healthy" or not. But some people want to work on problems that actually do require knowledge and should not have to have their discussions constantly vandalized. A "functional" venue one might say.