A few years back I had an interesting exchange with Catholic apologist Dr. Art Sippo.
When I recommended the works of Catholic historian Joseph Lortz on Luther, and pointed out that Lortz was pivotal to the change in Catholic scholarship toward Luther, Dr. Sippo stated:
"[Catholic historian joseph Lortz] was a Nazi just like Adolph Hitler. Both of them were Luther fans."
"You know, come to think of it, If Mr. Swan rally thinks that being a Nazi doesn't disqualify Fr. Lortz as a Luther expert, why doesn't he go right to the top and advocate the opinions of Adolph Hitler himself!"
"Mr. Swan wants us to believe that a man like Fr. Lortz who held to these "lofty ideals" can be trusted to interpret Luther correctly! Frankly, I would be embarrassed to be associated with him."
Well, if Dr. Sippo won't listen to me, perhaps he'll listen to his Pope:
Question: Where does Luther scholarship stand today? Have there been any attempts to research Luther's theology, beyond existing historical investigations?
Cardinal Ratzinger: Nobody can answer this question in a few sentences. Besides, it would require a special kind of knowledge which I do not possess. It might be helpful, however, briefly to mention a few names which represent the various stages and trends of Catholic Luther scholarship. At the beginning of the century we have the decidedly polemical work by the Dominican H. Denifle. He was responsible for placing Luther in the context of the Scholastic tradition, which Denifle knew better than anybody else because of his intimate knowledge of the manuscript materials. He is followed by the much more conciliatory Jesuit, Grisar, who, to be sure, encountered various criticisms because of the psychological patterns in which he sought to explain the problem of Luther. J. Lortz from Luxembourg became the father of modern Catholic Luther scholarship. He is still considered the turning-point in the struggle for an historically truthful and theologically adequate image of Luther. Against the background of the theological movement between the two world wars, Lortz could develop new ways of questioning which, subsequently, would lead to a new assessment of Luther.
Source (PDF alert)