Honestly, for some even reading part of the first paragraph will be enough to refute any argument against Dignitatis Humanae and calm their conscience.
DH #1 “…First, the council professes its belief that God Himself has made known to mankind the way in which men are to serve Him, and thus be saved in Christ and come to blessedness. We believe that this one true religion subsists in the Catholic and Apostolic Church, to which the Lord Jesus committed the duty of spreading it abroad among all men. Thus He spoke to the Apostles: “Go, therefore, and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things whatsoever I have enjoined upon you” (Matt. 28: 19-20). On their part, all men are bound to seek the truth, especially in what concerns God and His Church, and to embrace the truth they come to know, and to hold fast to it.
This Vatican Council likewise professes its belief that it is upon the human conscience that these obligations fall and exert their binding force. The truth cannot impose itself except by virtue of its own truth, as it makes its entrance into the mind at once quietly and with power.
Religious freedom, in turn, which men demand as necessary to fulfill their duty to worship God, has to do with immunity from coercion in civil society. Therefore it leaves untouched traditional Catholic doctrine on the moral duty of men and societies toward the true religion and toward the one Church of Christ…” (Vatican Website Translation)
Before we begin the defense of DH I want us to (re)-read the above quote from DH # 1. Thus, any claim that DH # 1 is going against the duty towards the true religion and one Church should be taken with a grain of salt. The document itself clearly recognizes in the first paragraph that it is dealing with subject matter previously spoken of authoritatively. It does not seek to change doctrine but develop it. Note the context. We are dealing with the nature that to worship God properly -as he wants- it has to be done with immunity from coercion. This is the development. States must have a duty towards the true religion, but this duty cannot jeopardize its true worship which must be without coercion.
Claim DH#2 says, “This Vatican Council declares that the human person has a right to religious freedom. This freedom means that all men are to be immune from coercion on the part of individuals or of social groups and of any human power, in such wise that no one is to be forced to act in a manner contrary to his own beliefs, whether privately or publicly, whether alone or in association with others, within due limits.” Yet, Pope Pius IX, Syllabus of Errors, Dec. 8, 1864, # 77: says, “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. Pope Pius IX, Syllabus of Errors, # 78: “Hence in certain regions of Catholic name, it has been laudably sanctioned by law that men immigrating there be allowed to have public exercises of any form of worship of their own.” – Condemned.
Response: First, DH#2 is not saying that the Catholic Church should not be the only religion in the state. It is basically realizing that we are in a post Catholic/Christian world. Most countries are not nor have been for a long time self proclaimed Catholic States. Early Christianity existed without the state or government. Middle Christianity after Constantine had State support as is just. Late, Christianity post reformation is all over the place or no state support. So that is where we are at. It is best that the State supports Catholicism as it is the truth, but most people in the State are not Catholic or don’t practice. So what do we do? Do we force people to become Catholic? DH #2 says NO! It says, we respect their freedom, as Pope Pius IX would agree. He was not saying we should force conversion. When society becomes Catholic again it will be time to stop the expansion of foreign religion once again. Yet, stopping the expression of foreign religion cannot go against or force people. God does not force belief it is a choice. Thus, no Catholic should ever do so also. Thus, It is expedient that the Catholic Church be the State religion, but the way to get there is not through forced conversion, but through changing of hearts. Now I hope, we can see that Pope Pius and Vatican II are on the same page. Pope Pius IX in the syllabus of errors was not defining or explaining teaching but simply listing errors. There is no reason we should expect his statements to have the same type of subtleties that Vatican II posses.
Claim: DH#3 Says that the state should be godless! Yet, many Popes have said that it should not be godless.
Response: Read DH#3 carefully. It says, “…Government therefore ought indeed to take account of the religious life of the citizenry and show it favor, since the function of government is to make provision for the common welfare. However, it would clearly transgress the limits set to its power, were it to presume to command or inhibit acts that are religious…” Thus, what you get is not godless, but a state that ought indeed to take account of the religious life of citizenry as it says. Yet, DH preserves the ancient law that the State cannot direct Catholic or other religious worship. (Think of King Saul and some of the Roman Emperors who tried to directly influence Church sacraments) The State is in charge of temporal ordering, and through this only indirectly concerned with religious affairs, as for the good of citizens. This indirect concern with religious affairs does not allow a State to command or inhibit religious acts (like Mass) because acts (like Mass) are the sole jurisdiction of the Church. The State ought to be concerned about the religious life of its people as DH#3 says, but it must do so in a way that does not violate the proper domain given to Church or religious leaders which is the moral authority and public worship authority.
Claim: DH#4 “…Religious communities also have the right not to be hindered in their public teaching and witness to their faith, whether by the spoken or by the written word. ..” Yet, many documents can be cited where other religions were forbidden from publishing documents in Catholic countries.
Response: We have to be careful to differentiae between the circumstances as to why and when those documents forbidding religious documents to be published were made. Fr. Harrison’s work cited and linked below is an excellent (but long) article on how DH did not break with tradition in this matter of religious publications. DH#4 is in fact a natural development and clarification of previous Papal statements forbidding certain publications. https://www.catholicculture.org/culture/library/view.cfm?recnum=8775
Due to the subtle arguments used on both sides of the debate I will not go into them here. If you want to calm your conscience you can read the complete and excellent defense referenced above.