As a media company and one of Americans' top sources of information, Facebook's de facto anonymity and general lack of responsibility for user-generated content make it easy for propagandists to exploit. Making matters worse, it isn't willing to impose tighter identification rules for fear of losing too many users, and it doesn't want to be held responsible in any way for content, preferring to present itself as a neutral platform.
So Zuckerberg has been trying to fix the problem by showing people more material from friends and family and by prioritizing "trusted publishers" and local news sources over purveyors of fake news.
But the Cambridge Analytica scandal shows people may not be OK with Facebook's data gathering, improved or not.
The scandal follows the revelation (to most Facebook users who read about it) that, until 2015, application developers on the social network's platform were able to get information about a user's Facebook friends after asking permission in the most perfunctory way. The 2012 Obama campaign used this functionality. So — though in a more underhanded way — did Cambridge Analytica.