[amarkov]

But it seems like decentralization would be a mortal blow to privacy. If we struggle to get a monolithic Facebook to treat our data responsibly, how could we possibly convince 500 decentralized Facebook nodes? (And why isn't it trivial for the NSA or FSB to copy the world's data by standing up node #238 under an alias?)

[Yetanfou]

Decentralised as in "run your own for your family and any friends who do not want to run their own", not as in "run the node for this geographical area". As long as the management boundaries coincide with the privacy boundaries - i.e. data within nodes belongs to a group of people who already share said data since they are in the same family or friend group - the scenario you picture here would not come to pass.

Of course there are several attempts at building a decentralised 'social' network like this, e.g. Diaspora and GNU Social. Thus far they have not taken off other than in limited circles.