15. Here We must include that harmful and never sufficiently denounced freedom to publish any writings whatever and disseminate them to the people, which some dare to demand and promote with so great a clamor. We are horrified to see what monstrous doctrines and prodigious errors are disseminated far and wide in countless books, pamphlets, and other writings which, though small in weight, are very great in malice. We are in tears at the abuse which proceeds from them over the face of the earth. Some are so carried away that they contentiously assert that the flock of errors arising from them is sufficiently compensated by the publication of some book which defends religion and truth. Every law condemns deliberately doing evil simply because there is some hope that good may result. Is there any sane man who would say poison ought to be distributed, sold publicly, stored, and even drunk because some antidote is available and those who use it may be snatched from death again and again?

16. The Church has always taken action to destroy the plague of bad books. This was true even in apostolic times for we read that the apostles themselves burned a large number of books.[23] It may be enough to consult the laws of the fifth Council of the Lateran on this matter and the Constitution which Leo X published afterwards lest "that which has been discovered advantageous for the increase of the faith and the spread of useful arts be converted to the contrary use and work harm for the salvation of the faithful."[24] This also was of great concern to the fathers of Trent, who applied a remedy against this great evil by publishing that wholesome decree concerning the Index of books which contain false doctrine.[25] "We must fight valiantly," Clement XIII says in an encyclical letter about the banning of bad books, "as much as the matter itself demands and must exterminate the deadly poison of so many books; for never will the material for error be withdrawn, unless the criminal sources of depravity perish in flames."[26] Thus it is evident that this Holy See has always striven, throughout the ages, to condemn and to remove suspect and harmful books. The teaching of those who reject the censure of books as too heavy and onerous a burden causes immense harm to the Catholic people and to this See. They are even so depraved as to affirm that it is contrary to the principles of law, and they deny the Church the right to decree and to maintain it.