“This shameful font of indifferentism gives rise to that absurd and erroneous proposition which claims that liberty of conscience must be maintained for everyone. It spreads ruin in sacred and civil affairs, though some repeat over and over again with the greatest impudence that some advantage accrues to religion from it. “But the death of the soul is worse than freedom of error,” as Augustine was wont to say.[ St. Augustine, epistle 166.] When all restraints are removed by which men are kept on the narrow path of truth, their nature, which is already inclined to evil, propels them to ruin. Then truly “the bottomless pit”[ Ap 9.3.] is open from which John saw smoke ascending which obscured the sun, and out of which locusts flew forth to devastate the earth. Thence comes transformation of minds, corruption of youths, contempt of sacred things and holy laws — in other words, a pestilence more deadly to the state than any other. Experience shows, even from earliest times, that cities renowned for wealth, dominion, and glory perished as a result of this single evil, namely immoderate freedom of opinion, license of free speech, and desire for novelty.
“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?
“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.[ Acts 19.] 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.”[Acts of the Lateran Council 5, session 10, where the constitution of Leo X is mentioned; the earlier constitution of Alexander VI, Inter multiplices, ought to be read, in which there are many things on this point.] 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.[Council of Trent, sessions 18 and 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.”[Letter of Pope Clement XIII, Christianae, 25 November 1766.] 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.” -Pope Gregory XVI, Mirari Vos, 15 August 1832
“We, therefore, while We declare that everything wisely said should be received with willing and glad mind, as well as everything profitably discovered or thought out, exhort all of you, Venerable Brothers, with the greatest earnestness to restore the golden wisdom of St. Thomas, and to spread it as far as you can, for the safety and glory of the Catholic Faith, for the good of society, and for the increase of all the sciences. We say the wisdom of St. Thomas; for it is not by any means in our mind to set before this age, as a standard, those things which may have been inquired into by Scholastic Doctors with too great subtlety; or anything taught by them with too little consideration, not agreeing with the investigations of a later age; or, lastly, anything that is not probable.” -Pope Leo XIII, Aeterni Patris, 4 August 1879
“Whatever, therefore, is opposed to virtue and truth may not rightly be brought temptingly before the eye of man, much less sanctioned by the favor and protection of the law. A well-spent life is the only way to heaven, whither all are bound, and on this account the State is acting against the laws and dictates of nature whenever it permits the license of opinion and of action to lead minds astray from truth and souls away from the practice of virtue.” –Pope Leo XIII, Immortale Dei, 1 November 1885
“If we are to avoid the errors which are the source and fountain-head of all the miseries of our time, the teaching of Aquinas must be adhered to more religiously than ever. For Thomas refutes the theories propounded by Modernists in every sphere, in philosophy, by protecting, as We have reminded you, the force and power of the human mind and by demonstrating the existence of God by the most cogent arguments; in dogmatic theology, by distinguishing the supernatural from the natural order and explaining the reasons for belief and the dogmas themselves; in theology, by showing that the articles of faith are not based upon mere opinion but upon truth and therefore cannot possibly change; in exegesis, by transmitting the true conception of divine inspiration; in the science of morals, in sociology and law, by laying down sound principles of legal and social, commutative and distributive, justice and explaining the relations between justice and charity; in the theory of asceticism, by his precepts concerning the perfection of the Christian life and his confutation of the enemies of the religious orders in his own day. Lastly, against the much vaunted liberty of the human reason and its independence in regard to God he asserts the rights of primary Truth and the authority over us of the Supreme Master. It is therefore clear why Modernists are so amply justified in fearing no Doctor of the Church so much as Thomas Aquinas.” -Pope Pius XI, Studiorum Ducem, 29 June 1923
“More than ever nowadays an extended and careful vigilance is necessary, inasmuch as the dangers of moral and religious shipwreck are greater for inexperienced youth. Especially is this true of impious and immoral books, often diabolically circulated at low prices; of the cinema, which multiplies every kind of exhibition; and now also of the radio, which facilitates every kind of communications. These most powerful means of publicity, which can be of great utility for instruction and education when directed by sound principles, are only too often used as an incentive to evil passions and greed for gain. St. Augustine deplored the passion for the shows of the circus which possessed even some Christians of his time, and he dramatically narrates the infatuation for them, fortunately only temporary, of his disciple and friend Alipius. How often today must parents and educators bewail the corruption of youth brought about by the modern theater and the vile book!” -Pope Pius XI, Divini Illius Magistri, 31 December 1929
“Minds of all, it is true, are affected almost solely by temporal upheavals, disasters, and calamities. But if we examine things critically with Christian eyes, as we should, what are all these compared with the loss of souls? Yet it is not rash by any means to say that the whole scheme of social and economic life is now such as to put in the way of vast numbers of mankind most serious obstacles which prevent them from caring for the one thing necessary; namely, their eternal salvation.” -Pope Pius XI, Quadragesimo Anno, 15 May 1931