Institutio Oratoria

It is eloquence

that snatches criminals from the penalties of the law, eloquence that from time to time secures the condemnation of the innocent and leads deliberation astray, eloquence that stirs up not merely sedition and popular tumult, but wars beyond all expiation, and that is most effective when it makes falsehood prevail over the truth.

The comic poets even accuse Socrates of teaching how to make the worse cause seem the better, while Plato says that Gorgias and Tisias made similar professions.

And to these they add further examples drawn from the history of Rome and Greece, enumerating all those who used their pernicious eloquence not merely against individuals but against whole states and threw an ordered commonwealth into a state of turmoil or even brought it to utter ruin; and they point out that for this very reason rhetoric was banished from Sparta, while its powers were cut down at Athens itself by the fact that an orator was forbidden to stir the passions of his audience.