Here's an example of the type of Roman Catholic apologetic Luther was up against.
Silvestro Mazzolini da Prierio, called Prierias was a Dominican. He was a leading Thomist and was appointed by Leo X to teach Thomist theology at the Latin School in Rome. Here are his fundamental presuppositions that informed his argumentation against Luther. As you read through them, try to imagine a Roman Catholic apologist defending these statements today.
"Without having an inkling that it was a religious question with Luther, Prierias, in order to draw out Luther's fundamentals, set forth in four theses the most extreme views on the infallibility of the Church, concluding that any one asserting that the Church could not do what she did (specifically regarding indulgences) must be adjudged a heretic." (Schaff)
1. Essentially the universal church is the assembly in divine worship of all who believe in Christ. The true universal church virtually is the Roman Church, the head of all churches, and the sovereign pontiff. The Roman Church is represented by the College of Cardinals, however, virtually it is the pope who is the head of the Church, though in another manner than Christ.
2. As the universal church cannot err when it decides on faith or morals, so also a true council cannot err if it does its best to know the truth, at least not in the end result - and that I understand under the inclusion of the head. For even a council can initially be mistaken so long as the investigation of the truth is still in process; indeed a council has sometimes erred: nevertheless it finally knows the truth through the Holy Spirit. Accordingly, the Roman Church and the pope cannot err when he in his capacity as pope comes to a decision, i.e., when he comes to a decision in consequence of his office and thereby does his best to know the truth.
3. He who does not hold to the teaching of the Roman Church and the pope as an infallible rule of faith, from which even Holy Scripture draws its power and authority, he is a heretic.
4. The Roman Church can establish something with regard to faith and ethics not only through word but also through act. And there is no difference therein, except that the word is more suitable for this than the act. In this same sense custom acquires the power of law, for the will of a prince expresses itself in acts which he allows or puts into effect. And it follows that as he is a heretic who wrongly interprets Scripture, so also is he a heretic who wrongly interprets the teaching and acts of the Church in so far as they relate to faith and ethics.
Corollary: He who says in regard to indulgences that the Roman Church cannot do what she has actually done is a heretic. [source]