I believe that you, a person with a strong interest technology, believe the consequences are (and perhaps always were) obvious.

But I disagree that if we went back in time and quizzed people clicking "yes" that the majority would really understand that recent events were the probable expected outcome of them clicking "yes".

There's a difference between consent and informed consent. And it was strongly in the interests of Facebook (and anybody who made an app using their APIs) to be very vague about the potential consequences.