> Doesn't it operate as a social network, where some content is available publicly? That would make it a bit different than email...
There's no technical reason that email isn't public, just social convention. Emails are like postcards, and the content is visible to all routers that they pass through on the way to their final destination.
In theory, we could have decided that email was an open discussion platform (more like USENET) with almost no technical changes.