Consider the following scenario:
Unlike FB, Google does have inherent advertising value. I want to buy a widget, I search Google, and Google returns hits, along with paid advertising that concerns widgets. Google does not depend so much on personal information from me in order to do this. I generally do not mmind this, as I am looking for widgets anyway. 'Course, I do limit the amount of information that I allow Google to gather about me - as a security precaution ...
Conversely, all FB has is personal information. It will have to develop algorithms to create "best guess" probabilties that I do or do not want a widget - based on the information in my account. It will then sell my information to its advertising clients - without any input from me.
If I start getting spammed on FB by advertisers for products I don't want - then I am going to limit the information that I want given out, or drop FB all together. As a result, advertisers are going to drop FB [ala GM] since they see no upside to it. No advertising - no bucks ...
Right on!
That's exactly what most adults will do (have done.)
But No one has mentioned the other elephant in the room. The facilitation of the exploding criminal industry of identity theft; hacking of facebook accounts and the nightmares than ensue. The main beneficiaries of facebook are internet criminals of all kinds.