"Fake news" isn't the problem, it's the symptom of a mainstream media landscape which has sacrificed its credibility for partisanship, activism, and sensationalism. People are willing to believe new sources because they don't know who to trust.
Which is a lesson in itself isn't it? How can we be sure there even exists an objective reality when not only can we not trust what we learn second hand, but also cannot trust our own senses or memory? We are in the awkward position of simultaneously needing to be skeptical of our understanding of the world while simultaneously having no choice but to act as though it were correct.
Where does mainstream end? Is HN mainstream? Reddit? Twitter? Breitbart? Fox? The problem with dichotomous categorization is it loses a lot of information. These are all offenders in vastly different ways, best not to lump and over generalize about them.
When people talk about the "mainstream media" in this context, they tend to mean established pre-web mass media - television, radio and newspaper, and any official web presence by these companies. So Reddit no, Twitter no, Breitbart no, Fox yes.
