I use the "outdoors" versus "indoors" analogy regarding free speech in the US. Outdoors you can say all kinds of stuff, on your own or public property, pursuant to not infringing on the rights of others, and with some other restrictions, most famously not falsely yelling "FIRE!" in a crowd.
But indoors in my home, you are my guest by my permission. And if I don't like your speech, or even the color of your shirt, I can require you to leave. You have no recourse, and no Constitutional right to remain under my roof and continue speaking, on any topic.
So it is with Internet online social sites. We visit them with the owner's permission.
At the same time, if you kick me out of your home because you say in front of other people I'm a thief, and I'm not a thief, then there may be grounds for charging you with slander, or defamation of character, or whatever is the appropriate charge in that jurisdiction. Likewise on the Internet, if you also boot me from your site on a false claim of my being a thief, and allow other site members to learn of that, slander charges may also apply. But First Amendment free speech rights would not be involved in either the home or Internet situations.