Social media should be considered common carriers, like telephone companies, delivery services, or transportation services.
An airline or UPS cannot just say "We don't like your politics so we will not ship your packages."
Social media is extremely similar to all these common carriers in that they are a "content" delivery mechanism. They do not decide what item is in a box or what message is in a phone call, they just distribute the box or phone call from the originator to the consumers. Similarly with social media content the social media company distributes content they have little control over through its distribution network. There is little different from a social media account than a (teletype?) conference telephone call with answering machines.