Basic Premise of the Book
The book makes a case that since mass media news outlets are now run by corporations, they are under the same competitive pressures as other corporations. The pressure to create a stable, profitable business invariably biases the kinds of news items reported, as well as the manner and emphasis in which they are reported. These biases occur despite the best efforts of the reporters and editors to fairly report all the newsworthy events.
The book further points out issues with dependancy of mass media news outlets upon major sources of news, particularly the government. If a particular outlet is in disfavor with a government, it can be 'shut out', and other outlets given preferential treatment. Since this results in a loss in news leadership, it can also result in a loss of readership/viewership, and thereby a loss of advertising revenue. This can result in outlets reporting news in a tone more favorable to the government and giving unfavorable news about the government less emphasis.
Opposing Viewpoints are Needed.
The documentary film Manufacturing Consent - Noam Chomsky and the Media was based in part on Chomsky and Herman's work; the remainder of the film serves as a biography of Chomsky.
see also corporatocracy