To quote Drucker, who paraphrased McLuhan;
"Did I hear you right," asked one of the professors in the audience, "that you think that printing influenced the courses that the university taught and the role of university all together." "No sir," said McLuhan, "it did not influence; printing determined both, indeed printing determined what henceforth was going to be considered knowledge."
Thus, this led to McLuhan's famous phrase that the
"medium is the message". Specifically, as we developed a new medium for human
communications, we dramatically altered the nature of the information that was
transferred and the way in which the human perceived what was "truth"
and what was not. The television generation of the 1960's was an clear example
of the impact of television versus film in portraying the war in Vietnam
as compared to the Second World War. The perception of these two events was
determined by the difference of the two media that displayed them to the pubic
masses. Television allowed for a portrayal that molded more closely to the
individual humans impact of the events as compared to films overview of the
groups involvement's. Both media deal with the same senses but they are
different enough to have determined two different outcomes of the wars.
This is ever more the case today as we see a multiplicity of media. The new media define what is "true". Thus one can argue that "fake news" is nothing more than an application of these new media. We have gone from the printing press to a mass collection of media in just a century. That means that we have gone from reading a newspaper written by some third party to an explosion of media and opinions created by individuals, and worse, by propaganda bots. The human receiver of this information fails to have the skills or even the intellectual training to ascertain truth and value.
McLuhan most likely never perceived this dramatic change.