Zuck did react but late and without actually challenging the core issue at hand: Facebook is a media company with a tech DNA. He is slowly coming to that realization but still running it as a tech company. As to your question on separating fake vs fact, Facebook has already started with their alerts (see example in my article). Is this enough ? Clearly not. News has been “mediated” since the days of town criers and the printing press kickstarted gazettes that were social networks in their day where news was literally cut and pasted from gazette to gazette. Read Andy Kessler’s How We Got Here for a more recent account that includes primers on the crossroads of tech and news.