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. 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.” 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. “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the material for error be withdrawn, unless the criminal sources of depravity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.” 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. (Gregory XVI, Mirari
Vos, 15-16 [August 15, 1832])