Multiplying examples of how public opinion is manipulated in democracies, Noam Chomsky invites us to think critically about political speeches. It also shows some reference books, such as Propaganda Edward Barneys, to go further in the exploration of manipulation techniques.
A passage was particularly marked page 82, as a conclusion of a long development: "Propaganda is to democracy what violence is to totalitarianism," that is to say a relatively effective way of falling asleep consciences . This seems also reach a point developed by Al Gore in the documentary "An Inconvenient Truth" (72nd to 74th minutes) to pass global warming for implausible hypothesis as fact is not called into question by climatologists.
In conclusion I can highly recommend reading this booklet;).