It may seem paranoid, but if there's one advantage of being paranoid it's this, I am hyper-vigilant and see the enormous potential on how to manipulate, entice and blackmail people with information I could obtain from someone's Facebook by hopes they or one of their friends "friend" me on there. It could range from destroying their friendships/relationships/job prospects to getting them arrested for a confessed crime, or a rare worse case, get them beaten up/killed even (if someone is already out for their blood and you just happen to let them know where they live). You could argue that before online social networking this happens and why should it be any different now? Well time is the difference, before it was a bit too time consuming and costly to even bother, but now that's no longer a problem.
So if I can think of cunning ways to abuse information to play people to my interests, surely I'm not the only one thinking that.