That's still not the point though.
How do I openly share social information with some people without sharing it with everyone? These principles are in conflict.
I did some work way back when FB got popular on the idea of using probabilistic data structures (ie, Bloom filters) to store contact lists, which could then be shared so that (in theory) only people who knew the same people would also know that they knew them. I built a FB app proving this could work technically.
But there are clear security issues with it - it gives a veneer of apparent privacy but doesn't stand up to attacks.
This is what everyone is talking about and the point you seem to be missing: you can't have this both ways. There is a conflict between privacy and openness.
Since you seem fixated on the crypto-payment thing: Monero mostly solves anonymous payments, but then what? Say I want to buy a pair of shoes with it - how do I stop someone knowing where to deliver it? Any attempt at solving this runs into the same problem: you have to tell someone the same thing you are trying to keep secret, and if that person is the attacker then the system falls to pieces.
