"What Zuckerberg has done is to substitute the largely uninformed opinions of one-third of the population as to what constitutes news for the judgments of thousands of trained journalists, most of whom have made collecting and reporting the news their careers."

These would be the 'judgments' of the 'trained journalists' who predicted Trump's winning the Republican nomination for President, right?    How about predicting that Bernie Sanders would be anything more than a minor footnote in the contest  against She  Who  Will soon be Anointed Queen of the Democrats?  The 'trained journalists' score on that one?

Seems to me that the 'largely uninformed opinions' (I think of them as votes) left those 'trained journalists' with egg on their faces.