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.

I'd go even further and say the the motivation isn't specifically to shape public opinion to your view, but simply to present the content in a way that doesn't create cognitive dissonance with your personal view. If you personally don't believe that a piece of information is relevant, then you leave it out. That piece might not be relevant to your own view of the subject, but could be crucial to an opposing view.

He actually has a fairly interesting segment on the reporting of strikes:

> The underlying trouble appears in the news through certain easily recognizable symptoms, a demand, a strike, disorder. From the point of view of the worker, or of the disinterested seeker of justice, the demand, the strike, and the disorder, are merely incidents in a process that for them is richly complicated. But since all the immediate realities lie outside the direct experience both of the reporter, and of the special public by which most newspapers are supported, they have normally to wait for a signal in the shape of an overt act. When that signal comes, say through a walkout of the men or a summons for the police, it calls into play the stereotypes people have about strikes and disorders. The unseen struggle has none of its own flavor. It is noted abstractly, and that abstraction is then animated by the immediate experience of the reader and reporter. Obviously this is a very different experience from that which the strikers have. They feel, let us say, the temper of the foreman, the nerve-racking monotony of the machine, the depressingly bad air, the drudgery of their wives, the stunting of their children, the dinginess of their tenements. The slogans of the strike are invested with these feelings. But the reporter and reader see at first only a strike and some catchwords. They invest these with their feelings. Their feelings may be that their jobs are insecure because the strikers are stopping goods they need in their work, that there will be shortage and higher prices, that it is all devilishly inconvenient. These, too, are realities. And when they give color to the abstract news that a strike has been called, it is in the nature of things that the workers are at a disadvantage. It is in the nature, that is to say, of the existing system of industrial relations that news arising from grievances or hopes by workers should almost invariably be uncovered by an overt attack on production.