What makes you think that user-moderated content won't be as toxic as algo-driven one? Look at reddit for example - the vast majority of content out there is posted to cause outrage, and people parrot it across the rest of the site.
Reddit isn't decentralized. The "moderators" play enforcers for the admins, to push their agenda and cleanse the site of any content the management doesn't want to see. Outrage is their business model, it leads to increased interactions between users (i.e. flame wars) and so they spend more time on the site. Any community or mod that doesn't play along is removed, thus in the major subs you can think of them as directly working for the company, although unpaid. The users are NOT in charge, there is a crazy amount of political censorship on reddit. In the end that leaves the echo chamber it is now. Your example demonstrates how the authoritarian style of managing social media suppresses free speech but does nothing to reign in toxicity. Facebook and Twitter are similar toxic echo chambers.
On an actually decentralized platform the radicals would still be there, but so would many other voices. Where users can't be banned for "wrongthink", communities must convince their audience with arguments or fear losing supporters. The chilling effect would be gone. A truly decentralized site would have plenty of communities the individual user doesn't agree with - just like in real life. And just like in real life users can deal with it by staying away.
Removing the_donald sub was ridiculous especially when compared to equally if not more objectionable rhetoric on main subs like /r/politics. Additionally if you want to get rival subs banned on reddit you just post and report objectionable material icognito. Reddit is a dumpster fire of juvenile , woke idiocy now and I rarelt visit anymore. That said some of the content on the_donald was just as idiotic but if you are going to allow one you have to allow the other.
