He actually touches on this as well:
> There is a very small body of exact knowledge, which it requires no outstanding ability or training to deal with. The rest is in the journalist's own discretion. Once he departs from the region where it is definitely recorded at the County Clerk's office that John Smith has gone into bankruptcy, all fixed standards disappear. The story of why John Smith failed, his human frailties, the analysis of the economic conditions on which he was shipwrecked, all of this can be told in a hundred different ways. There is no discipline in applied psychology, as there is a discipline in medicine, engineering, or even law, which has authority to direct the journalist's mind when he passes from the news to the vague realm of truth. There are no canons to direct his own mind, and no canons that coerce the reader's judgment or the publisher's. His version of the truth is only his version. How can he demonstrate the truth as he sees it? He cannot demonstrate it, any more than Mr. Sinclair Lewis can demonstrate that he has told the whole truth about Main Street. And the more he understands his own weaknesses, the more ready he is to admit that where there is no objective test, his own opinion is in some vital measure constructed out of his own stereotypes, according to his own code, and by the urgency of his own interest. He knows that he is seeing the world through subjective lenses. He cannot deny that he too is, as Shelley remarked, a dome of many-colored glass which stains the white radiance of eternity.
I recommend giving the book a read at some point if you have the chance (there's also a free audio book up on YouTube). It's a very thought provoking journey through how public opinion gets formed, and the myriad of different elements at play shaping them.