Ask HN: Did Facebook really do something wrong?
Now the platform itself is open and can be used by others in their apps to get user data. In such a case, the user himself approves sharing his data on Facebook with the app. This is what happened in the case of Cambridge Analytica. Users used a 3rd party app which collected data. They voluntarily did it. The app then shared it with Cambridge Analytica. The app developer got data from users and used it in ways he didn't disclose to his users.
Facebook makes close to no money from these third party apps. I have written apps in the past which ended up collecting user information which just sits in my database. I don't see how Facebook can prevent exploitation of this data as it can't be monitored. They could just shut down the pipe but I believe that will again make many people mad. The app developer is at fault.
Given above, I feel its the app developer at fault and not Facebook.
TL;DR Facebook advertising doesn't leak user information. Cambridge Analytica's approach would fail if people simply stopped using 3rd party apps.