Laudator Temporis Acti

Cicero, On the Nature of the Gods 1.23.63 (tr. H. Rackham):

Since as for Protagoras of Abdera, the greatest sophist of that age, to whom you just now alluded, for beginning a book with the words 'About the gods I am unable to affirm either how they exist or how they do not exist,' he was sentenced by a decree of the Athenian assembly to be banished from the city and from the country, and to have his books burnt in the market-place: an example that I can well believe has discouraged many people since from professing atheism, since the mere expression of doubt did not succeed in escaping punishment.

Nam Abderites quidem Protagoras, cuius a te modo mentio facta est, sophistes temporibus illis vel maximus, cum in principio libri sic posuisset: 'De divis, neque ut sint neque ut non sint, habeo dicere', Atheniensium iussu urbe atque agro est exterminatus librique eius in contione combusti; ex quo equidem existimo tardiores ad hanc sententiam profitendam multos esse factos, quippe cum poenam ne dubitatio quidem effugere potuisset.

Clarence A. Forbes, "Books for the Burning," Transactions of the American Philological Association 67 (1936) 114-125 (at 118):

The book of Protagoras was only the first of a long line that were burned for religious reasons. Religion has always been the chief cause for the deliberate destruction of books, and the histories of western religion have about them a pungent smell of smoke.

Forbes, p. 125:

For the true art of unjust censorship to develop, the world had to wait until the modern era. We of the twentieth century live in glass houses, and had best be chary of throwing stones.

Burning Books (May 10, 1933)