If you are a programmer, you have like 15 answers to this question per programming language. Lots of very smart people who get high on their own supply and speed run to crankdom.
Brianna Wu? Shes the first that comes to mind
There's that post by shipwreck (or one of their alts) about how Prigozhin was a modern Trotsky in the sense of some competent Russian commander with a weird charisma and a dedicated fanbase while also not being able to stop saying unhinged shit. Like Trotsky, Prigo tried and failed to undermine the current leader in charge, and like Trotsky, Prigo eventually got owned.
Richard Dawkins comes to mind, a formerly rather progressive atheist fending against Christian fundamentalism, who basically turned into an islamophobe transphobe.
Banned? DM Wmill to appeal.
No anti-nautilism posts. See: Eco-fascism Primer
Vaush posts go in the_dunk_tank
Dunk posts in general go in the_dunk_tank, not here
Don't post low-hanging fruit here after it gets removed from the_dunk_tank