That position, I've observed, evokes objections from two ends of the spectrum. At one end are those who believe that said development of doctrine has indeed reversed a "definitive" and pertinent teaching, thus discrediting the Magisterium's claims for itself. At the other are those who believe that the Church has not substantively developed doctrine on this point at all, so that violently coercing heretics would be little more problematic than fighting other threats to the public weal, such as terrorists. On the former end, one finds a priest of the Anglican "Continuum," Fr. Matthew Kirby, whom I debated on this topic last month; on the latter, one finds Catholic blogger I. Shawn McIlhinney of Rerum Novarum (henceforth 'ISM' for brevity), whom I debated on this topic a few weeks ago. After a hiatus for the election, ISM has now replied to that post of mine. I now reply in turn.
Much of ISM's post arises from and/or clarifies mutual misunderstandings and would thus be of little general interest. My focus here shall be on what I had said was the core issue: the interpretation of a key passage from Vatican II's Declaration on Religious Freedom, Dignitatis Humanae. Here is that passage:
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.
I claimed, and maintain, that the concluding phrase 'within due limits' should be taken to modify not the entire sentence in which it occurs but only the phrase 'in association with others'. In addition to the argument I gave in my previous post, I point out that it would be unreasonable to claim that, according to the Fathers of Vatican II, there are "due limits" period to refraining from forcing rational adults to act contrary to their beliefs—as though forcing people to act against their consciences were just an imprudent idea some of the time, rather than intrinsically wrong and thus wrong all the time. Indeed, the question what the "due limits" should be arises only when people act in association with others. For only then can we even talk about acts which harm society, such as publicly professing heresy, and which thus should be prevented or punished by coercive means. That was the issue for the medieval Church when her officials justified torturing and/or executing heretics. Merely being heretical in one's beliefs was not the issue; the issue was the real or imagined social harm the heretic did by professing their heresy publicly.
As best as I can make out, what ISM takes to be his view to the contrary is not contrary to mine at all. His exposition of DH on this question clearly indicates that the moral question about coercing heretics only arises when the objectionable actions of heretics are public; and as a matter of concrete fact, such acts fall within the competence of the state, and thus of legal coercion, only when they are performed in association with others. So I don't think ISM and I are really disagreeing about what DH meant. The only remaining question is whether what DH meant is a development beyond medieval ideas, so that religious freedom must now be understood to apply as much to non-Catholics as Catholics. I think the answer is obvious.