John Milton's Aeropagitica was penned in response to the Licensing Order of 1643, which in effect gave Parliament the power to exercise what has become known as prior restraint on controversial or subversive publications. Milton argued that the prior restraint of publications was a practice more befitting a Catholic government, and provides examples from classical antiquity and the current state of affairs in Catholic countries (including an account of a meeting he had with Galileo) to demonstrate his argument. But above all, Milton appeals to the principle of intellectual freedom to argue that squelching ideas at their source is sinful:
...as good almost kill a Man as kill a good Book; who kills a Man kills a reasonable creature, Gods Image; but hee who destroyes a good Booke, kills reason it selfe, kills the Image of God, as it were in the eye.
Milton is not arguing for free speech or expression. He admits that heretical or especially blasphemous ideas ought to be punished if expressed publicly in print. But he also argues that attempts to shield people from bad ideas in an attempt to make them virtuous will actually weaken their virtue. He also argues that reason is a God-given virtue, and that censorship attacks that virtue at its source. "Give me the liberty to know, to utter, and to argue freely, according to conscience, above all liberties,” Milton argued.