The difficulty was not what the declaration said but what the papacy had said before. In 1832 Gregory XVI had called freedom of conscience an absurd and erroneous opinion, indeed a madness. In 1864 the Syllabus of Errors condemned the proposition that every man is free to embrace the religion he believes true by the light of reason. The Catholic states of the nineteenth century had drawn the practical conclusion, and Spain still had a confessional constitution when the council opened.
The council's answer was development rather than contradiction: the earlier condemnations addressed an indifferentism that denied any obligation to seek truth, whereas the declaration addresses immunity from coercion. Whether that distinction holds is the question the text has never escaped. The strongest objection came from within: Archbishop Marcel Lefebvre and the group of bishops around him voted against, and the Society of Saint Pius X, which he founded in 1970, has made this document the centre of its refusal of the council. It remains the hardest single point in the discussions between the Holy See and that society.
The wider consequences were considerable. American constitutional practice, long viewed with suspicion in Rome, became a model rather than a concession, and the theologian John Courtney Murray, silenced in the 1950s for arguing the case, drafted much of the final text. The Holy See has since argued for religious liberty as a universal civil right in international forums, which it could not coherently have done before 1965.