[forgotmypw17]

You can make all those things private only to the extent that you trust each individual participant. The larger the group, the more likely a leak can happen. The other defense is limiting what you share with the network, and selectively encrypt.

There's a lot of benefit to be gained from sharing the social graph (or at least statistics based on it, which, however, can sometimes be reversed unexpectedly)

At the moment, we have the exact opposite of the situation you're asking for--anyone who's got a database and 10 bucks can see everything, while those for whom the data is the most relevant and potentially beneficial have very limited access... so even full transparency is an improvement, IMO.