Good points. Scale and centralization make the world of Facebook et. al. a much thornier problem. They've become Too Big To Fail™, with all that entails. Not to mention antitrust issues, but that's a digression in itself.

I see some hope in federated systems, and, for that matter, old-school forums that have survived. Usenet still sputters along, but it's not what it was before spammers ruined it.