What anti-establishment stuff has he done? All of the negative things I see people mention about him are just general asshole behaviour rather than things that annoy the establishment.
Censorship is the tool of the establishment. Free speech gives power to the people. That's as anti-establishment as it gets.
You've fallen for a warped definition of free speech and censorship that is endlessly regurgitated by NPCs.
(For this reason, in a world where Musk already controlled Twitter, I would oppose anything that increased his leverage w.r.t. Facebook, because yes, you're correct that Musk's biases are not harmless.)