34 Doctrines such as these, which cannot be approved by human reason, and most seriously affect the whole civil order, Our predecessors the Roman Pontiffs (well aware of what their apostolic office required of them) have never allowed to pass uncondemned. Thus, Gregory XVI in his encyclical letter Mirari Vos , dated August 15, 1832, inveighed with weighty words against the sophisms which even at his time were being publicly inculcated-namely, that no preference should be shown for any particular form of worship; that it is right for individuals to form their own personal judgments about religion; that each man's conscience is his sole and all-sufficing guide; and that it is lawful for every man to publish his own views, whatever they may be, and even to conspire against the State. On the question of the separation of Church and State the same Pontiff writes as follows: "Nor can We hope for happier results either for religion or for the civil government from the wishes of those who desire that the Church be separated from the State, and the concord between the secular and ecclesiastical authority be dissolved. It is clear that these men, who yearn for a shameless liberty, live in dread of an agreement which has always been fraught with good, and advantageous alike to sacred and civil interests." To the like effect, also, as occasion presented itself, did Pius IX brand publicly many false opinions which were gaining ground, and afterwards ordered them to be condensed in summary form in order that in this sea of error Catholics might have a light which they might safely follow.(22)
Source: Immortale Dei (Vatican.va)