Not sure if it's caused by power-hungry mods, the upvote/downvote dynamics or political polarisation, but you can often quickly make out specific "opinions" that are somehow magically shared by everyone posting in a particular subreddit.
The UX also actively supports this by de-emphasizing individual users and emphasizing subreddits as the primary "personalities" of the platform. This goes so far that on r/all, the names of the individual users who posted the threads aren't even shown anymore. All you see is subreddits.
That together with some "supermods" moderating large fractions of the popular subreddits and a recent post on HN of another redditor who experienced shadowbanning makes me seriously wonder how authentic the discussions you see on r/all really are.
An interesting and notable thing in this context is how for any given interest represented on reddit there is actually an entire ecosystem of subs. There's the main one, the decade-old mod schism one, the "circlejerk" parody one, the "True" one that takes itself more seriously, the more recent schism that allows slurs, the one for memes about the interest, a few to many for various subdivisions or specializations within the interest, various vestigial zombie schisms and misspellings that may or may not just redirect to one of the others.
Each of these will have elements of its own culture and history and jargon and in-jokes, but drawn from the same pool of subject matter and all in some way referencing or revolving around the biggest one, even if only in opposition to it. All will share some mods with at least some others and most users will frequent more than one of them.
What you end up coming up against is identity. Each sub needs a reason for itself to exist and so members create that meaning by enforcing the norms, referencing the jokes, and socializing new members into the history and protocol. HN works exactly like this too btw; it is culturally a subreddit, even if hosted elsewhere with slightly different game mechanics.
Imagine holding a companies website hostage you work for free on unless they run their company how you want them to.
I guess it is a combo of additive fake grassroots and bans.
It feels like, at some point, a point of view becomes law and all dissent disappears.
I mean three close friends in some anarchist 100-voters-in-total party don't agree as much as reddit users seems to do.
Why not? If billions of people can be in a religion then surely millions can be in a subreddit with some religion-like properties.
I think there is probably not a clear and useful line between manipulation and moderation. There's no neutral moderation, all mod policies and actions are towards a certain goal & vision for how the community should be. I'm not sure what fake grassroots would be but I think the upvotes and awards account for that: people know what will be rewarded and the rewards turn posting into a performance.
Anyway I'm going to point this out again because it's useful and interesting: HN behaves in these same ways to about the same degree as any large sub does. The alignment on etiquette, culture, accepted belief and punishment for deviation from it is very strong here. This indicates to me that this is somehow an emergent characteristic of large self-selecting online communities.