While it is true that the Vatican II document on Religious Liberty, Dignitatis Humanae, departed from the more recent Catholic tradition of mandating Catholicism as a state religion, it was perfectly in accord with ancient Catholic Tradition on freedom of conscience regarding religious decisions.
Why the change from previous papal encyclicals?
Simply put, previous papal teaching dealt with a world where Catholic emperors and kings ruled and were expected to enforce the Catholic religion as the only religion of the state. Non-Catholic Christians in the 16th century were to be subject to arrest, imprisonment, or even death.
The French bishops were delighted in the 17th century when King Louis XIV of France took the toleration Edict of Nantes and ripped it apart, saying only Catholicism should be tolerated in France. Then he battered down the Protestant stronghold of LaRochelle and forced most of them into clandestine practice of their faith. The bishops were less amused when he told them that he was like the Sun and the Catholic Church would be like the moon which could only operate from his power and authority.
After the revolutions of Europe and the West, after democracy, and later after communism, world governments ceased to have Catholic monarchs. Actually, they began to have at times virulently anti-Catholic governments who considered it their duty to persecute or even wipe out the Catholic religion.
In such a brave, new world, it made no sense, in fact it would appear hypocritical and even stupid for the Catholic to appeal for a cessation of persecution while not advocating the same for others who also suffered under government anti-religious coercion. During Vatican II, the Catholic Church, then, turned to the thought of the ancient Fathers who had to live in the age of persecution and martyrdom.
The Church woke up and smelled the coffee. It was no longer in the age of Constantine and Theodosius. There were no more emperors riding to its defense. Like the Church of the catacombs, it appealed to the thought of St. Justin Martry and Tertullian, who appealed in those ancient days for Catholics and all people to have freedom of conscience.
This was not a reversal of Tradition, from the apostles, but of tradition, from the age of a Catholic Christendom which no longer existed. It was not a change of revealed dogma, but of a tradition of pastoral teaching which had always dealt severely with other faiths, but which had to face a new reality.
“But” the protest went, “error has no rights.” Yes, true. However, as Fr. John Courtney Murrary said when speaking of Justin and Tertullian, “although error has no rights, people do have rights, even when they choose in their conscience to follow error.” Or as Justin said almost 2,000 years ago, “nothing is more contrary to religion than constraint..” and “compulsion is not an attribute of God.”
Vatican II returned to an ancient patristic line of thought of religious liberty, in order to deal with a world which was similar now to that age of the persecutions.
For further reading see: