For SocialMedia to work, that is to say, where strangers on the Internet can upload their works and have them be distributed by some entity that runs a social media site (or “provides a social media service”?), we need to absolve them from liability in limited ways.
Liability comes in because some works may not be distributed because of copyright violations (famously: music, videos); or because it violates state secrets (remember WikiLeaks); or other criminal law (notoriously: sexual abuse of various kinds); or because they constitute libel and defamation; and so on. What this usually boils down to is that we force the people doing the distributing to make their best effort in cleaning up the mess after the fact. So anybody is free to upload whatever, but the people running the sites employ moderators and algorithms to remove offending content and to prevent reuploading of said content. In order to prevent the abuse of these rules and tools, there also needs to be a process to object to and appeal these decisions. We end up with a semi-automated PreLegalSystem?.
Moderators are expensive, services are free, money is generated by ads or sale of privacy relevant data, margins are small … and so we end up with underpaid human moderators in countries where labour is cheap and labour protection is slim, and with endless labyrinthine automated solutions full of automated mails, bots, and ArtificialStupidity.
One solution to this is to decentralize. Split services up until they are manageable. A small association where people know each other, where personal ties, maybe even friendship, bind people together. This results in social groups where moderation happens initially (when new people join), but soon enough trust replaces moderation and so the system works, but it doesn’t scale.
This is why smaller systems like PubNixes or a Fediverse instance is easier to manage and moderate than a mega-site like YouTube. There simply aren’t enough moderators to do that, given the economic constraints of the current system: free access, ad-based income, profit increasing with scale.