I agree with the need to seriously study the text and writings of such individuals (rather than modern books about them) if someone wants to know what they believe. There is too much danger of basing an opinion or even pronouncing judgment upon flawed or out-of-context "reporting." There is also a danger in searching through those books simply to find "sound bites" that will be used as an indictment for hellfire.
Why?
All of those men and organizations are flawed. This includes the early "reformers." This includes the modern biographers. This even includes the anabaptists. They were human beings confined to this side of the "glass darkly." While some may have been flawed on more insignificant matters, they were still flawed by their humanity nonetheless. Not all reformers, anabaptists or even earlier believers were pious men.
One thing that is clear from the Epistles is that there was a propensity to "get things wrong" even at such an early stage in Church history. If you notice in the Book of Acts, even Paul and Barnabas had a disagreement so sharp that they split company. Paul rebuked Peter -- a man who walked with Christ, wrote portions of the New Testament and was a focal point of the Gospels and the Book of Acts -- over a gross doctrinal flaw. It seems that even the apostles weren't immune from their flawed humanity.
By the time (~100 A.D.) John was having a revelation of Jesus Christ on the Isle of Patmos, five of the seven churches of Asia were given instructions about various flaws within them. And, of course, the Epistles includes strong words and even rebukes about situations in the churches -- including some that were quite disturbing (remember I Corinthians 5?).
Such flaws shouldn't surprise us. After all, none of us are perfect. We are still confined to this side of that "glass darkly" in which we live in this life. I believe that many marriages end because someone is looking for or expecting a "perfect" spouses (which, of course, is quite interpretive). Oddly enough, I think that many churches and believers split company for the same reason. They are looking for a "perfection" in the church that is either literally "perfect" or at least partially modeled after what they think to be true. Yet, not even the early church was perfect (at least, not when the New Testament was written down).
One thing to remember is that we are perpetually changing. Each of us -- and every other believer -- is changing as we mature to Christ. We should always remember this when we meet with others. We aren't the same people that we were when we first came to Christ (except, hopefully, in our love for Him). We have "grown" in knowledge and understanding through prayer and study of the Word of God.
Now, many believers belonged to other "Church" organizations before they came to Christ. When they met the Lord, their "understanding" was not what it is now...and not what it will be a few years from now. Why? We are continuously maturing during our journey through the "wilderness of this world." Some people, like Martin Luther, were Catholics before coming to Christ. Their doctrinal vision may not have been quite so "20-20" when they first came to the Lord...and it may have taken some time to focus on doctrinal truths as presented by Scripture.
Others have changed in their interpretation of what the Word of God instructs. There were believers a few hundred years ago who believed in or ignored the grotesque concept of slavery. Something that should have been so obvious from Scripture was viewed as acceptable. Many believers, like Martin Luther or the reformers, wrote what they believed at a given moment of time. Like everyone, they may have changed over time. Hindsight (and Eternity) is often the "20-20" that we think that we possess in the present.
For instance, in BEYOND THE CROSS AND THE SWITCHBLADE, David Wilkerson mentioned that he no longer held a "hard line" approach when it came to television. He had spoken about a need to get rid of the TV in the original CROSS AND THE SWITCHBLADE book. Yet, years later, Wilkerson wrote that he and his family would sit down and watch "family westerns" like Bonanza. A decade later (in SET THE TRUMPET TO THY MOUTH), Wilkerson once again wrote about the dangers of having a television in the home.
Now, if a person were to describe David Wilkerson's perspective on the "television" issue, it would be somewhat skewed to assert that he embraced television. It would be more correct to say that, at one point, David Wilkerson believed that it was okay to have a television in the home. And, of course, I don't know what Brother Wilkerson believed when he died last year. My point is simply that his view changed over time.
So, in terms of Martin Luther or the other reformers (or ANYONE else for that matter), it is important to approach the topic with this in mind. Their views may have changed over time as they matured in Christ.
In the past, there have been some heated discussions about Charles Finney. Finney's writings have been analyzed, dissected and criticized many times. Some are willing to embrace much of what he said. Others are unwilling to accept anything that he said. And still, others are quite bold in declaring the man a "heretic." There is little grace offered in terms of how his views may have changed over time. And, of course, we can't seek clarity by speaking to the man himself. This is true of all men who have died. We can't ask them to elucidate on such matters.
So, when it comes to the writings of all men, I suggest that we approach those works with the knowledge that NONE of them are perfect. This includes the reforumers, the anabaptists and every man who have sermons included on this website. We have to simply glean what we can from what they said or wrote. We must test everything and hold on to the good (I Thessalonians 5:21). After all, our faith does not hinge upon the writings or teachings of any of these men or organizations. Our faith is only in Christ Jesus His Word.
With this in mind, it would be beneficial to avoid spreading accusations about others. If we are flawed or even slightly incorrect in what we say (or how we present it), we may end up unwittingly bear false witness against someone else...even if we think it is for a good reason.