The heretic Martin Luther remarked, “No one must be constrained. Liberty is the very essence of faith.” Such a statement, which has rooted itself in Western Democracies in our Post-Enlightenment society, is nothing other than a grave evil.
His Holiness Pope Gregory XVI's words in Mirari Vos serve as a guide for our times and a warning to turn away from liberty of conscience:
Now We consider another abundant source of the evils with which the Church is afflicted at present: indifferentism. This perverse opinion is spread on all sides by the fraud of the wicked who claim that it is possible to obtain the eternal salvation of the soul by the profession of any kind of religion… ‘without a doubt, they will perish forever, unless they hold the Catholic faith whole and inviolate’…Image Source: Pope Gregory XVI Visiting the Church of San Benedetto at Subiaco by Jean-François Montessuy (French, 1804–1876)
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. 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" 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.