I don't think its fair to blame FB on the decay of democracy in the information age. Surely Twitter is also to blame them. I think the blame is on the users. Its not possible to be perfectly informed. It is possible to keep your mouth shut if you don't know something for sure. Perhaps its the fact that in real life, to say something you need to say it to someone's face and on social media you don't have that social weight to carry. This brings about people more likely to share misinformation. If this is the case, its not the fault of social media, rather the fault of internet culture. More personal responsibility is the solution. Not an improved ML system to detect fake news.
It is a problem inherent in the structure of most social media companies. And Facebook is the most significant social media company, and thus contributor to the problem.