There absolutely is precedent that a private company or private property can be considered a “public forum” and therefore has to respect free speech / assembly rights.
The Colorado Supreme Court ruled in Bock v Westminster Mall that because they allowed a range of activities at the mall and also allowed government offices (recruiters for the armed forces) to set up kiosks that they had become a “latter day public forum” and could not deny free speech / assembly rights. This case in particular is pertinent.
The US Supreme Court ruled in Marsh V Alabama that owners of a private company town could not prohibit the distribution of religious tracts because they had treated the town as a public area.
Basically if a private business does certain things that act like a “public forum” then they become a public forum.
Facebook, Twitter, and YouTube allows business to use them, private citizens to use them, cities, etc. They also allow the government to use them. There are also a wide range of activities. Community postings, fund raising, etc. additionally, unless a person keeps their content “private”, the content is visible to anyone without an account, meaning it is “public”.
They have become a de facto “town square” and must not prohibit free speech activities. There is grounds for class action against all of the big 3.
Good point.
There are also the treatment of public utilities that are monopolies.
How ironic that a private baker can be fined for not putting a gay message on a cake, but an open public forum is not punished for prejudicial editing and blocking.