via Chomsky's "We Own the World":
So we had the usual kind of debate going on, which illustrates a very important and pervasive distinction between several types of propaganda systems. To take the ideal types, exaggerating a little: totalitarian states' propaganda is that you better accept it, or else. And "or else" can be of various consequences, depending on the nature of the state. People can actually believe whatever they want as long as they obey. Democratic societies use a different method: they don't articulate the party line. That's a mistake. What they do is presuppose it, then encourage vigorous debate within the framework of the party line. This serves two purposes. For one thing it gives the impression of a free and open society because, after all, we have lively debate. It also instills a propaganda line that becomes something you presuppose, like the air you breathe.