I don't mean there's a single centralized moderating authority overseeing everything, but rather the general tools and mechanisms used for moderation on the Internet are centralized and undemocratic. They produce groups with authoritarian power structures and norms. Those groups get larger over time with no limit on their size. When they get large enough, they fight over which one gets to run a country. This is how modern democratic countries can turn authoritarian very fast, and it's already happening.
When I say "group", I don't mean an actual Facebook group or subreddit (it could be, though). I mean a group of intellectually/ideologically homogenous people. They may be distributed across many subreddits and comment sections. Forums/subreddits/servers can be separate entities in form, but not in substance. Two Discord servers that moderate content the same way are the same group in this context.
Moderation is not just for posters. It also affects lurking viewers because it changes what they will see. If a post is deleted by a moderator, then that moderator has decided for the viewers what they can and cannot see.
Up/down voting (aka likes/dislikes) is a hidden form of moderation as well. People's likes and dislikes are deciding what other people are more likely to see because upvoted posts get to the top of the feed. Recommendation and ranking algorithms do the same thing.
I'm not making a statement about who has nobler goals, be it the ad companies or Putin or the US gov or the people here on HN. I'm saying that the concept of centralized moderation on the Internet is itself the problem. Regardless of what or whose goals these tools serve, they're bad because they coagulate people into intellectually and ideologically homogenous groups, and there is no group size limit due to the practically infinite connectivity of the Internet. This will create nasty real-world consequences in the long run. But we can defuse this by moving all moderation and ranking to the client-side.