They are not public platforms, though. Not anymore public than a Starbucks. Just because "the public" can walk through a store's unlocked doors doesn't make the place public property. Same with social media. Just because "the public" can log into the platform's system doesn't make the place public.

Social media does, in my view, publish the content they host. It's not like the telephone, where you establish a direct connection to your audience and the mediator gets out of the way. When you post something to social media, there are three separate steps that happen:

1. You send the content to the SM company.

2. The SM company does some kind of processing on the content.

3. The SM company publishes that content (or not) somewhere on their site.

These things happen pretty much instantaneously, but they are still happening. Posting to Social Media is more like writing a Letter to the Editor of the newspaper. They receive the letter, decide whether to include it in the paper, then include it in the paper.