Pope Leo XIII, Immortale Dei: “The Almighty, therefore, has given the charge of the human race to two powers, the ecclesiastical and the civil, the one being set over divine, and the other over human, things. Each in its kind is supreme, each has fixed limits within which it is contained, limits which are defined by the nature and special object of the province of each, so that there is, we may say, an orbit traced out within which the action of each is brought into play by its own native right. … One of the two [civil power] has for its proximate and chief object the well-being of this mortal life; the other [ecclesiastical power], the everlasting joys of heaven. Whatever, therefore in things human is of a sacred character, whatever belongs either of its own nature or by reason of the end to which it is referred, to the salvation of souls, or to the worship of God, is subject to the power and judgment of the Church. Whatever is to be ranged under the civil and political order is rightly subject to the civil authority.”
The civil authority has no power over things pertaining to “the salvation of souls, or the worship of God.” Civil authority can only act with coercive power in religious matter when it is acting as an arm of the Church, as an agent of the Church’s coercive power.
A non-Catholic state lacks any coercive power to regulate matters pertaining to religion and therefore lacks the coercive power needed to suppress errors in matters of religion. The necessary result is that the citizens of a non-Catholic state cannot be forbidden from practicing a false religion or spreading religious errors.
This is what Dignitatis Humanae teaches. Nowhere does it teach that a Catholic state is unable to suppress false worship if it is acting as an arm of the ecclesiastical power. DH speaks only of the civil authority, qua civil authority. What this shows is that DH is simply repeating the teaching of Leo XIII and only has the appearance of contradicting tradition. Why has this not been clarified when it would have been so easy for the power that be to do so?