if the point of social media was just to talk to others, we have many other ways to do that. if it was to post publicly, we have blogs etc. and we can message people links to sites with a note, then talk about it.
what's special is the virality. and making it decentralized means no third party has final say on that virality. the public decides what's popular. what needs to be seen.
it's the power of mass media but put in the control of the public. revolutionary.