I do not understand how you derived that from your previous statements. Mastodon is a self-regulated network and I would say it is precisely set up to diverge into a plethora of echo chambers that can go as extreme as the members allow it to be (which, as is obvious from your example of usenet, is very extreme). That may not be specifically algorithmically enforced, but it is definitely part of the very concept of it. I see no way how something like Mastodon will magically self-moderate in the sense that extreme ideas will be suppressed and countered. You just won't see them.
It's not hard to understand the difference between algorithms pushing content to you and you choosing what to read yourself.
Echo chambers will always exist in some form or another, it is human nature to find safety in bubbles, but when a software platform and its CEO/board abuse their position to manipulate users then we have a problem on our hands.
The ultra wealthy who lose their minds and brainwash their followers to use them as soldiers should all be treated the same, whether it was Henry Ford and his newspaper/books, Osama in his cave, Murdoch and his "news" network, Putin and his private armies and troll farms, or Trump and MAGA, or Musk and his Muskrat army. If you encourage them they will grow worse and worse and worse.
It is nearly impossible to become ultra wealthy and maintain sanity. 99% of the ultra wealthy will always become extremists.
But I don't think they should be censored. Censoring them will allow them to argue that there is some "plot against freedom" and all other stupid conspiracy theories. We know these these madmen profess to fight for freedom but they are liars.
Instead of censoring, prosecute financial fraud.
Shine a light on their activities every day, including their private networks and financial interests. If stocks are being manipulated with false promises, if markets are being manipulated, if money is being laundered, if bribes are being paid - this is how you prevent the wealthy from abusing society.
In the name of "economic growth" we have seen almost no regulation or prosecution or audits for years. Over half of Musk's promises and manipulations are no different from Elizabeth Holmes and Trevor Milton's fraud.