[From "Dignitatis Humanae – Vatican II’s Declaration on Religious liberty"]

Vatican II’s Declaration on Religious Liberty was without question the most notorious of all the documents of Vatican II. In order to understand why Vatican II’s teaching on religious liberty is heretical one must understand the Catholic Church’s infallible teaching on the issue.

It’s a dogma of the Catholic Church that States have a right, and indeed a duty, to prevent the members of false religions from publicly propagating and practicing their false faiths. States must do this to protect the common good – the good of souls – which is harmed by the public dissemination of evil. This is why the Catholic Church has always taught that Catholicism should be the only religion of the State, and that the State should exclude and forbid the public profession and propagation of any other.

We will now look at three propositions that were condemned by Pope Pius IX in his authoritative Syllabus of Errors.

Pope Pius IX, Syllabus of Errors, Dec. 8, 1864, # 77: “In this age of ours it is no longer expedient that the Catholic religion should be the only religion of the state, to the exclusion of all other cults whatsoever.” – Condemned.[62]

Notice, the idea that the Catholic religion should not be the only religion of the State, to the exclusion of other religions, is condemned. That means that the Catholic religion should be the only religion of the State and that the others should be excluded from public worship, profession, practice and propagation. The Catholic Church doesn’t force nonbelievers to believe in the Catholic Faith, since belief (by definition) is a free act of the will.
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However, it teaches that States should forbid the propagation and public profession of false religions which lead souls to Hell.
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In Quanta Cura, Pope Pius IX also condemned the idea that every man should be granted the civil right to religious liberty.
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Vatican II teaches that religious liberty should be a civil right, which is directly condemned by Pope Pius IX. Vatican II also says that this right to religious liberty applies to public, as well as private, expression; and that no one should be prevented from the public expression or practice of his religion. The teaching of Vatican II is direct heresy against the infallible teaching of Pope Pius IX and a host of other popes. The teaching of Vatican II on religious liberty could literally have been added to the errors of the Syllabus of Errors condemned by Pope Pius IX.

Benedict XVI admits here that Vatican II’s teaching (which he adheres to) is directly contrary to the teaching of the Syllabus of Errors of Pope Pius IX. In other words, he just admitted that Vatican II’s teaching is contrary to the teaching of the Catholic Magisterium. One could hardly ask for more of a confirmation that the teaching of Vatican II is heretical. In his book, Benedict XVI repeats this again and again, calling the teaching of Vatican II “the countersyllabus,” and saying that there can be no return to the Syllabus of Errors!
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Vatican II says that the State exceeds its authority if it dares to prevent religious activity. This is totally heretical.

Here we see Pope Leo XIII (simply reiterating the consistent teaching of pope after pope) teaching that the State not only can, but should curtail and forbid the rights and privileges of other religions to perform religious acts – exactly the opposite of what Vatican II declared. Such public acts, false opinions and false teachings should be repressed by public authority (the State), according to the teaching of the Catholic Church, so that souls are not scandalized or enticed by them.
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To understand this better let’s give an example: If a State were presented, for instance, with Muslims and Jews holding their religious services and celebrations in a public place (even if they were not disturbing the peace or infringing on any private property or upsetting the public order at all), the State could and should (according to Catholic teaching) repress these services and celebrations and send the Jews and Muslims home (or would arrest them, if the law were well established) since they scandalize others and could cause others to join these false religions. The State would tell them their obligation to be Catholic before God and try to convert them by directing them to the Catholic priests, but it wouldn’t force them to do so. This is an example of the clear distinction between 1) forcing one to be Catholic, something the Church condemns, since belief is free and 2) the State’s right to repress false religious activity, something the Church teaches.
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Vatican II’s heretical teaching on religious liberty is precisely the reason why, following Vatican II, a number of Catholic nations changed their Catholic constitutions in favor of secular ones! The Catholic constitutions of Spain and Colombia were actually suppressed at the express direction of the Vatican, and the laws of those countries changed to permit the public practice of non-Catholic religions.
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We can see that the second section of Article 6 of the 1945 Constitution was replaced by that of the 1967 precisely in order to bring the laws of Spain into agreement with the declaration of Vatican II! Perhaps this revision of Catholic laws in a Catholic country, which was made in order to conform to the new religion of Vatican II, illustrates more than anything else the forces at work here. Spain went from a Catholic nation to godless one, which now gives legal protection to divorce, sodomy, pornography and contraception, all thanks to Vatican II.