From this poisoned source of indifferentism flows that false and absurd, or rather extravagant, maxim that liberty of conscience should be established and guaranteed to each man—a most contagious error, to which leads that absolute and unbridled liberty of opinion which for the ruin of Church and State spreads over the world, and which some men, by unbridled impudence, fear not to represent as advantageous to the Church. ‘And what more certain death for souls,” says Saint Augustine, “than the liberty of error!” On beholding them thus, indeed, take away from men every rein able to restrain them in the paths of truth, hurried as they already are to ruin by a nature inclined to evil, we may say in truth that there yawns that pit of the abyss, from which Saint John be- held ascending a smoke that obscured the sun, and locusts to lay waste the earth. Thence, in fact, the instability of minds; thence the ever increasing corruption of the young; thence, in the people, the contempt of sacred rights and holiest laws and things; thence, in a word, the saddest scourge that can ravage States, since experience attests, and the remotest antiquity teaches, that cities powerful in wealth, dominion, and glory perished by this sole evil—the unbridled liberty of opinions, the license of public discourse, the passion for changes.

With this is blended the liberty of the press—the most fatal liberty, an execrable liberty, for which there never can be sufficient horror, and which certain men dare so loudly and earnestly to demand and extend everywhere. We shudder, Venerable Brethren, when We consider the monstrous doctrines, or rather prodigies of error with which We are overwhelmed; errors disseminated far and wide by an immense multitude of books, pamphlets, and other publications, [blogs?], small indeed in bulk, but enormous in perversity, giving rise to the malediction which covers the face of the earth and causes our incessant tears.

...But very different has been the discipline of the Church in regard to the extinction of bad books from the very days of the Apostles, who, We read, burned publicly a great number of books. To be convinced of this, it will suffice to read attentively the laws passed on this matter in the fifth Lateran Council, and the constitution published soon after by Leo X, Our predecessor of happy memory, to prevent what had been happily invented for the increase of faith and the propagation of useful arts becoming perverted to the very opposite, and becoming an obstacle to the salvation of the faithful.