In Part One we saw the important sort of distinctions that must be made when we speak of Christ as Head of the Church and of all Men, and we concluded with the observation that Protestant critics usually misunderstand this sort of thing - as for example when they suggest that disagreements among Catholics about Magisterial teaching contradict what the Church says about itself. The short answer to that is, "Sorry, but you are mistaken."
The Church teaches that all Catholics must sincerely believe everything that the Church proposes for their belief. But the Church does not say that every Tom, Dick, and Harry - every poor and uneducated and illiterate Catholic - must consequently become a theologian in order to be saved. It is sufficient for a Catholic's faith to be implicit: that is to say, it is sufficient that a Catholic sincerely and genuinely intends to believe all that the Church teaches. Consequently - although it is obviously better to be able to do so - the Catholic who cannot say a word in explanation of the Nicene Creed is no less my brother Catholic than St. Thomas. He is formally Catholic, even if he may not be materially so in this respect. There is a measure of potentiality in his apprehension of the truth, although he is still Catholic in actuality.
So with regard to DV, we must charitably say that those who disagree about its meaning sincerely intend to believe what the Church teaches: they are formally united, even if they materially (and unfortunately) disagree. The fact remains, however, that DV teaches the truth. But even if one is inclined to be uncharitable, the most he can say is that there may be so-called Catholics who willfully reject what the Church teaches. But such men cannot reasonably called Catholics. They formally deny her doctrine and consequently sever themselves from her fellowship.
The argument takes a slightly different turn, however. It is supposed that Catholics can't get "infallible answers" on a whim from the Magisterium, and consequently their position is no better than that of the Protestant. But this is to misunderstand things. In the first place, God does not promise us "infallible answers" to just any question that we may have, and we neither need nor merit them. There will always be things that we do not understand simply because we are finite and prone to error. This means that it is wrong-headed to demand "infallible answers" to everything. We're not going to get them, and even if we did we wouldn't understand them all. The fact is, however, that we can and do get the answers that we need from the Magisterium, starting with our priests and bishops.
This necessarily differs from the Protestant's situation as it is usually presented (and certainly as it is represented in, for example, the Westminster standards). There is no room for formal and material distinctions there. There is no room for understanding the difference between objective availability of the truth by way of the Magisterium and its subjective apprehension. Black or white, on or off. The uncertainty that they have concerning essential matters of truth is a defect betraying the weakness of their position precisely because of how they say their position "works" with respect to the discovery of the truth: on their own terms, it fails. It is a systemic problem, not simply a problem of subjective apprehension or mere human weakness. They tell us that the Holy Spirit guides them to the truth, but there are very, very few things upon which all Protestants agree. Well, either the rest of their differences do not matter (in which case their disunity is truly scandalous) or they do. In my judgment there are things about which they disagree which cannot credibly be described as matters of indifference.
Lastly, as Martin points out in commenting on Part One, there is a legitimate sense in which we may say that everyone is implicitly Christian: the same sense in which we say that Christ is the Head of all men. To some this will seem to be universalist, as I pointed out, but only to those who are unable or unwilling to distinguish between potentiality and act, between the formal and material, between the objective and the subjective. To say that doesn't mean that every God-hater is destined for glory, but until the day he dies he is at least a Christian in potentiality.