It's still possible, and useful, to talk about these things, in the context of a private company, especially much of what he said happened. The concept of social media is new. It's ok to talk about that new thing, in order to understand it and what it's doing to society as a whole.

Nobody is arguing that constitutional rights directly apply here. They're arguing that free speech is important, especially when the government has been pushing around that private company: https://www.forbes.com/sites/emmawoollacott/2021/07/15/gover...