It has always been the Church's policy to extirpate heresy.
Pope Pius VIII, Traditi Humilitati, 1829: “The heretics have disseminated pestilential books everywhere, by which the teachings of the impious spread, much as a cancer. To counteract this most deadly pest, spare no labor.”
This was also practised against Luther and other Protestant heretics.
Pope Leo X, Exsurge Domine, 1520: “Moreover, because the preceding errors and many others are contained in the books or writings of Martin Luther, we likewise condemn, reprobate, and reject completely the books and all the writings and sermons of the said Martin, whether in Latin or any other language, containing the said errors or any one of them; and we wish them to be regarded as utterly condemned, reprobated, and rejected. We forbid each and every one of the faithful of either sex, in virtue of holy obedience and under the above penalties to be incurred automatically, to read, assert, preach, praise, print, publish, or defend them. They will incur these penalties if they presume to uphold them in any way, personally or through another or others, directly or indirectly, tacitly or explicitly, publicly or occultly, either in their own homes or in other public or private places. Indeed immediately after the publication of this letter these works, wherever they may be, shall be sought out carefully by the ordinaries and others [ecclesiastics and regulars], and under each and every one of the above penalties shall be burned publicly and solemnly in the presence of the clerics and people.”
And it didn't stop at burning books...
Pope Leo X, Exsurge Domine, 1520, ex cathedra: “Some of these errors we have decided to include in the present document; their substance is as follows: ...33. That heretics be burned is against the will of the Spirit. ...No one of sound mind is ignorant how destructive, pernicious, scandalous, and seductive to pious and simple minds these various errors are, how opposed they are to all charity and reverence for the holy Roman Church who is the mother of all the faithful and teacher of the faith; how destructive they are of the vigor of ecclesiastical discipline, namely obedience. This virtue is the font and origin of all virtues and without it anyone is readily convicted of being unfaithful.”
Many who call themselves Catholics recoil at the teaching of the Church on burning heretics, however, that is because they are not looking with the eyes of faith but are as godless men who perceive only the corporal.
Consider that a murderer deserves death for sowing death, but how much more serious is the destruction of souls compared to the body?
St. Jerome, Homilies on the Psalms: “The doer of evil has, indeed, killed his own soul; but the heretic — the liar — has killed as many souls as he has seduced... Every heretic is bloodthirsty, for every day he spills the blood of souls.”
St. Thomas Aquinas, Summa theologiae II-II, q. 11. a. 3: “Therefore if forgers of money and other evil-doers are forthwith condemned to death by the secular authority, much more reason is there for heretics, as soon as they are convicted of heresy, to be not only excommunicated but even put to death.”
St. Peter Canisius, doctor of the Church, admonishes rulers for not fulfilling their duty of administering justice and protecting the people with the sword.
“Herein magistrates offend, when they bear the
sword in vain, and are not, as they are called, God’s ministers and
revengers unto wrath, to those that behave themselves wickedly or
Nevertheless, the Holy Roman and Universal Inquisiton of the Holy Office was quite lenient for it never condemned anyone as a heretic unless he admitted to being one. The liar Galileo escaped death by concealing his heresy and was therefore branded vehemently suspect of heresy.
Pope Pius IX tackles the root of the error of freedom of the press and condemns the Second Vatican Council with his apostolic authority a century in advance.
Pope Pius IX, Quanta Cura (#’s 3-6), Dec. 8, 1864, ex cathedra: “From
which totally false idea of social government they do not fear to
foster that erroneous opinion, most fatal in its effects on the
Catholic Church and the salvation of souls, called by Our predecessor,
Gregory XVI, an INSANITY, namely, THAT ‘LIBERTY OF CONSCIENCE AND
WORSHIP IS EACH MAN’S PERSONAL RIGHT, which ough to be legally
proclaimed and asserted in every rightly constituted society; and that
a right resides in the citizens to an absolute liberty, which should
be restrained by no authority whether ecclesiastical or civil, **whereby
they may be able openly and publicly to manifest and declare any of their
ideas whatever, either by word of mouth, by the press, or in any
other way. But while they rashly affirm this, they do not understand
and note that they are preaching liberty of perdition… Therefore, BY
OUR APOSTOLIC AUTHORITY, WE REPROBATE, PROSCRIBE, AND CONDEMN ALL THE
SINGULAR AND EVIL OPINIONS AND DOCTRINES SPECIALLY MENTIONED IN THIS
LETTER, AND WILL AND COMMAND THAT THEY BE THOROUGHLY HELD BY ALL THE
CHILDREN OF THE CATHOLIC CHURCH AS REPROBATED, PROSCRIBED AND
CONDEMNED.” (Denz. 1690; 1699)
Statements to a similar effect are almost countless, here is one more:
Pope Pius XI, Allocution, December 20, 1926: “Catholics may not support, favor, or read papers which are edited by men whose writings are in notable opposition to Catholic doctrine in faith and morals...”
I also recommend all Protestants read Exsurge Domine and consider how merciful the Church was to Luther despite the enormous evil he was doing.