For anyone interested in the subject, I highly recommend Walter Lippmann's Public Opinion. It was written 100 years ago, but it's one of the best books on the media (and public opinion in general) that I've read, and the vast majority of the book accurately describes problems we have today. A couple of excerpts:
> Circulation is, therefore, the means to an end. It becomes an asset only when it can be sold to the advertiser, who buys it with revenues secured through indirect taxation of the reader...A newspaper which angers those whom it pays best to reach through advertisements is a bad medium for an advertiser. And since no one ever claimed that advertising was philanthropy, advertisers buy space in those publications which are fairly certain to reach their future customers. One need not spend much time worrying about the unreported scandals of the dry-goods merchants. They represent nothing really significant, and incidents of this sort are less common than many critics of the press suppose. The real problem is that the readers of a newspaper, unaccustomed to paying the cost of newsgathering, can be capitalized only by turning them into circulation that can be sold to manufacturers and merchants. And those whom it is most important to capitalize are those who have the most money to spend. Such a press is bound to respect the point of view of the buying public. It is for this buying public that newspapers are edited and published, for without that support the newspaper cannot live. A newspaper can flout an advertiser, it can attack a powerful banking or traction interest, but if it alienates the buying public, it loses the one indispensable asset of its existence.
And:
> This is the plight of the reader of the general news. If he is to read it at all he must be interested, that is to say, he must enter into the situation and care about the outcome. But if he does that he cannot rest in a negative, and unless independent means of checking the lead given him by his newspaper exists, the very fact that he is interested may make it difficult to arrive at that balance of opinions which may most nearly approximate the truth. The more passionately involved he becomes, the more he will tend to resent not only a different view, but a disturbing bit of news. That is why many a newspaper finds that, having honestly evoked the partisanship of its readers, it can not easily, supposing the editor believes the facts warrant it, change position. If a change is necessary, the transition has to be managed with the utmost skill and delicacy. Usually a newspaper will not attempt so hazardous a performance. It is easier and safer to have the news of that subject taper off and disappear, thus putting out the fire by starving it.
The whole thing is worth reading. It's free on Project Gutenberg, and there's also a free audiobook of it on Youtube.