Why Twitter and cable news make us stupid

From Gustave Le Bon's The Crowd: A Study of the popular Mind

The violence of the feelings of crowds is also increased, especially in heterogeneous crowds, by the absence of all sense of responsibility. The certainty of impunity, a certainty the stronger as the crowd is more numerous, and the notion of considerable momentary force due to number, make possible in the case of crowds sentiments and acts impossible for the isolated individual. In crowds the foolish, ignorant, and envious persons are freed from the sense of their insignificance and powerlessness, and are possessed instead by the notion of brutal and temporary but immense strength.

Given to exaggerations in its feelings, a crowd is only impressed by excessive sentiments. An orator wishing to move a crowd must make an abusive use of violent affirmations. To exaggerate, to affirm, to resort to repetitions, and never to attempt to prove anything by reasoning are methods of argument well known to speakers at public meetings.