They didn’t ban him for anything he wrote. They banned him for the speech at the January 6 rally where he said protest PEACEFULLY AND PATRIOTICALLY. People came to the rally on January 6 to protest peacefully. And that is their constitutional right. There was no reason to ban Trump. The New Twitter has revealed that Donald Trump was permanently banned despite not violating ANY Twitter rules; that the execs, especially Roth and Gadde, were looking for reasons to ban him for a long time.
I agree that the reasons for banning weren't genuine. But that doesn't mean Trump couldn't have avoided the ban if he'd spoken more carefully. I don't agree that it's tech platforms' constitutional right to remove politicians, though. The First Amendment guarantees free speech, and with obvious exceptions such as threats and libel, written content should be allowed freely on tech platforms that act as a public square.