I think, (without having read more than a third of the book) that the authors point was that amateur sources and written content now threatens to overshadow legitimate sources and informational content and that it takes an astute and critical reader to be able to accurately discern real information.
When I hear this problem being discussed, I've never understood how this is supposed to differ from the state of affairs in the past. There has always been ignorant nonsense out there, much of it written in legitimate newspapers and the like. All the internet has done is made it easier for more people to put their ignorant nonsense out there, while at the same time providing the astute and critical reader with a wealth of information to fact-check what they do read.
If I'd read some unsubstantiated claim in a newspaper or pamphlet 20 years ago, there would often have been be little I could do to ascertain its accuracy without dedicating a considerable amount of time to research. Now I can sometimes find out in five minutes through judicious use of Google.