Except online, all platforms are privately owned. Hence you often get de facto censorship. You can technically say something not allowed on those platforms, but then find there's no way to draw any attention to this content/those views. It's like living in a company town where anything the administration don't like isn't allowed.

It's a problem with freedom of speech and private property in general, and why some people have considered the idea of treating large social platforms as closer to utilities rather than businesses.