It's because they sell information (everything you do on facebook) and allow clandestine access (basically "black ops" or operations not officially recognized by the us government, typically intelligence.) and cooperate with "foreign dictators" such as in Egypt. So they know more about you than anyone else, and with that information can do a hell of a lot.
Plus, they make shitty mass-produced generic time-consuming games. That's reason enough right there.
Name something that they can do with the information on a generic facebook page that is bad. I'm not saying there is nothing they can do, I just don't know.