I have used passages from Plato to illustrate these points. His text is politically controversial, if not downright negative: everyone can see the absurdity of Plato's statement that the mixolydian mode should be banned as it would have a damaging influence on the development of character.
My second reason for writing De Staat is a direct contradiction of the first: I deplore the fact that Plato was wrong. If only it were true that musical innovation could change the laws of the State!