That doesn't work because it's not just what you share with the social networks but what others share about you and how they're able to link those little facts

That doesn't work because it's not just what you share with the social networks but what others share about you and how they're able to link those little facts to create a full picture. (Or what the social networks collect on you from other places.) Facebook had a leak ~3 years ago that showed it: http://www.zdnet.com/article/anger-mounts-after-facebooks-shadow-profiles-leak-in-bug/ http://www.zdnet.com/article/anger-mounts-after-facebooks-sh... but there have been darker efforts to do this since at least 2006 or so that I've found.