What's a private setting? When companies like twitter make their content available to users without requiring a login and password they are not providing a private setting. They are a public forum. That's what I would argue.
Furthermore, since their moderators are paid employees they are responsible for their actions and they can't claim that their employees discrimination isn't their responsibility.
Shadowbanning should also be considered a deceptive trade practice. Its primary intent is to deceive the user of the service.