Those who read the press of their group and listen to the radio of their group are constantly reinforced in their allegiance. They learn more and more that their group is right, that its actions are justified; thus their beliefs are strengthened. At the same time, such propaganda contains elements of criticism and refutation of other groups, which will never be read or heard by a member of another group…Thus we see before our eyes how a world of closed minds establishes itself, a world in which everybody talks to himself, everybody constantly views his own certainty about himself and the wrongs done him by the Others - a world in which nobody listens to anybody else.

Jacques Ellul