A problem for Protestants, especially those who call themselves Reformed Protestants and attempt to closely associate themselves with the magisterial Reformers Martin Luther and John Calvin, is the need to defend these two men at any cost.
In particular, Martin Luther said some really ugly things during his life, especially about Jews. His views on Jewish people seemed to have changed over his life from tolerance and a desire for them to come to know Christ, to all-out hatred and a desire for them to be murdered.
You then have to defend his derogatory remarks about the the book of James, Revelation, and the other New Testament books whose canonicity he doubted. Read all of his attacks on these books here in his preface to the these books, which he relegated to the end of his Bible. Excerpt on Revelation:
About this book of the Revelation of John, I leave everyone free to hold his own opinions. I would not have anyone bound to my opinion or judgment. I say what I feel. I miss more than one thing in this book, and it makes me consider it to be neither apostolic nor prophetic.
For myself, I think it approximates the Fourth Book of Esdras; 8 I can in no way detect that the Holy Spirit produced it.
Moreover he seems to me to be going much too far when he commends his own book so highly — indeed, more than any of the other sacred books do, though they are much more important — and threatens that if anyone takes away anything from it, God will take away from him, etc. Again, they are supposed to be blessed who keep what is written in this book; and yet no one knows what that is, to say nothing of keeping it. This is just the same as if we did not have the book at all. And there are many far better books available for us to keep.
For me this is reason enough not to think highly of it: Christ is neither taught nor known in it. But to teach Christ, this is the thing which an apostle is bound above all else to do; as Christ says in Acts 1, “You shall be my witnesses.” Therefore I stick to the books which present Christ to me clearly and purely. (emphasis mine)
It is argued that Luther eventually removed this preface and so (presumably) changed his mind about these books’ canonicity, but that does not mean we should ignore his words here; rather, they give us a better understanding at this time of Luther’s disposition toward the Church and the Bible (would you dare to pass judgment on one of St. John the Beloved Disciple’s inspired works?)
After that, his statements about the sacraments (more Catholic than you think! (these are written by an Anglican professor)) have to be ignored or explained away, as do his (dangerously Catholic) beliefs on Mary’s perpetual virginity and other Marian doctrines (can anyone say, “Mother of God”?), and finally his support of polygamy.
If you are a Protestant who reveres Luther, these facts (especially on Jews) present a difficult problem, and the best solution seems to be to ignore this particular dark side of his heart, but that is a hard to do when you hold him up to be the brilliant reformer of the corrupt Church, a man allegedly extremely faithful to Christ, but Christ taught us to love our neighbors (including Jews).
Why should we look to him and his teachings as being those of Christ when he himself spewed such hateful venom at the Jewish people?
This is the problem with putting so much stock into one person (other than Jesus Christ). Catholics would apparently have the same problem with their Saints, but in actuality we do not because, though a saint might have exhibited heroic virtue in his or her life, all of our important doctrines and teachings and practice of the faith do not depend upon any one or two people, as Protestants have to depend on Luther and Calvin.
So it might be that St. Augustine had some inaccurate ideas at one time on some issues, but what St. Augustine says is not necessarily what Christ’s Church discerned to be truth. The same for St. Jerome, St. Thomas Aquinas, and so on. All of our key doctrines are not pinned on any one of these saints, even though they all contributed important ideas to the truth of God discerned within the Church.
But Luther and Calvin, in schisming from the Church, pitted themselves against the Church and all of her Fathers, Doctors, and great saints, male and female. Luther’s judgments, condemnations, and corrections of the great Fathers of the Church are well-documented (see here and here for some of his statements).
The Saints were declared saints because they humbled themselves within Christ’s Church and persevered to the end of their lives in submitting their own insights, thoughts, and teachings to Her, whom Christ promised to defend against all enemies.
Martin Luther was not a demon from Hell sent to ruin us all. He was a man. Like me, like you, with faults and virtues, sometimes a weak faith and sometimes a strong one, with doubts and hopes and dreams and disappointments. I think the truth of him is somewhere between the hagiographies and the demonizations. The Catholic Encyclopedia has what seems to me to be a fairly objective description of the important events of his life and the actions he took. Also, I have heard good things from my friend Phil about Alister McGrath’s book Christianity’s Dangerous Idea: The Protestant Revolution, so I recommend that (though it covers much more than just Luther). McGrath is an Anglican.
I end by encouraging you, whether Protestant or Catholic (or other), to learn for yourself about Luther and Calvin and consider the weight that they must bear under Protestantism.