But the simple fact that between US corporations and the US government, privacy abuses have been so bad (although admittedly still better than some other countries) that there is no chance people would willingly opt into any such system. Even if the current incarnation is honest, there is 0% chance that it will stay that way, for one reason or another.
Everyone older than a teenager should remember the whole Google 'do no evil' thing, and many of us honestly hoped that they would stay that way. Unfortunately, reality had a way of crushing Google's desires to be honest and innocent, and to make a long story short they now they play hard ball just like everybody else.
The idea is great. But the reality would have never worked. Just like both Communism and Democracy.