Facebook has managed to give news to people who generally arent interested in the news. Theres a whole swathe of Britain who has never had any interest in politics, society, history, education, who have suddenly had all of this information thrown at them.
Many of these people arent equipped to think critically and work out where the truth lies and because of this have been duped by divisive and corrosive content. When they are shown images of lines of middle eastern looking men and told their security is under threat by immigrants, they arent equipped to evaluate its merit.
In short, social media targets the most vulnerable minds, in a way newspapers never could.