Am I "censoring people" if I ask a customer to leave my restaurant and never return while he is in the middle of a loud racist rant?

Facebook and Twitter are not critical infrastructure. Nobody has to use them. They are private platforms their owners invited you to. I choose not to use these services, and anyone else who doesn't like them is free to do the same.

People do not have the choice to avoid using telephone or mail services, which is why they are regulated as common carriers. It is nearly impossible to function in modern society without access to mail and telephone service. The argument for net neutrality rests on the idea that general internet access is also a requirement in order to be a functional member of society.