Thomas acknowledged that private entities usually aren't constrained by the First Amendment but added that the First Amendment may apply on a private company's online platform "if the government coerces or induces it to take action the government itself would not be permitted to do, such as censor expression of a lawful viewpoint."
This is not even remotely the right point in the stack for content moderation. Twitter, Facebook and other platforms are not public spaces affording guarantees of free speech. People removed from the platform, I would argue are not even censored. They are free to continue to spread whatever message they would like on the Internet. No one can silence your ability to spread your message on the internet. That's what makes it great, and sometimes terrible. Using a personal domain, or any other service where they have not been removed for violating terms of service or code of conduct, everyone is free to put whatever they'd like out there. No one is entitled to access on another service.