Relying on cognitive limitations of your subjects to get agreement you wouldn't get if the subjects were fully-informed is fraudsters' domain.

And since the article is called "What Data Does Facebook Collect When I’m Not Using Facebook?" I'd like to point out that I never agreed to Facebook tracking my browsing habits. I couldn't say they were clear and forthcoming about their tracking because we never met. Are you saying they wouldn't do it without my explicit permission? Because that would be news.