John Milton opposed censorship for many reasons but one thought sticks in the mind, that “he who destroys a good book, kills reason itself” (1644)
Found in: Areopagitica (1644) (Jebb ed.)
When Parliament did not relax the law requiring the prior censorship of books after the English Revolution had broken out but in fact passed an ordinance requiring the licensing of the press in 1643, John Milton urged it to reconsider:
Freedom of Speech
…books are not absolutely dead things, but do contain a potency of life in them to be as active as that soul was whose progeny they are; nay, they do preserve as in a vial the purest efficacy and extraction of that living intellect that bred them. I know they are as lively, and as vigorously productive, as those fabulous dragon’s teeth: and being sown up and down, may chance to spring up armed men. And yet, on the other hand, unless wariness be used, as good almost kill a man as kill a good book: who kills a man kills a reasonable creature, God’s image; but he who destroys a good book, kills reason itself, kills the image of God, as it were, in the eye.