Part of the problem is that unless the consent is very explicitly communicated so that there is no doubt, it has the potential to pose substantial risks to people.

When I was at school, I remember a student that went abroad that had to get assistance to find new housing after she'd been thrown out by her host family just for receiving a letter from the political youth organization she was a member of at home in Norway, for example (she was a member of Socialist Youth - the youth organization of a mainstream left wing party that has since been part of ruling coalitions, nothing remotely extremist, but too much for her particular host family).

That was a benign situation compared to what might happen if Facebook starts outing peoples political views to people they may have no expectation of sharing their views with, but who has physical access.

I don't this process will survive contact with the real world very long before they get sued.