This is arguable. Our country is changing massively, and because of the network effect[1], social media platforms condense to only a few winners, currently mostly Facebook and Twitter I believe. This oligopoly[2] means that a handful of sites basically run what is considered the internet for most people.
In America, we have a constitutional right to free speech. If in our country, most people speak solely on one of these sites, then why shouldn't our constitutional rights extend onto them?