> If a private corporation gets to decide by virtue of ownership - property rights granted by societal contract to begin with - then they have unilateral, unaccountable power over society.

Again, I have the opposite interpretation. If the government gives a private organization property rights, the government is the holder of power over society. The organization has authority over what the government gave it the rights to, and the government gave them the right (with section 230) to moderate their property in the way they are now.