There is a HUGE difference between a platform / utility and a private business. The cake / flower shops never refused to sell their products to people with whom they disagreed. They did refuse to be required to participate in an event with which they disagreed. Big difference.
As for Mail Chimp / Twitter / et al, if they are private companies and can restrict access, then they can also be held liable for content as a publisher. If they want no liability for content, then they are a platform / utility like the phone company and cannot restrict content.
Why the Trump administration has not taken a big stick to this constant abuse is surprising and disappointing.
Jim restricts content. Should he be liable for what people post here?