God has only ever had one Person He used who had no flaws, namely the Lord Jesus Christ.
We celebrate the Protestant Reformation. We admire and respect the men (and women) God used in what was the greatest move of God in Church history, outside of the book of Acts. And yet, even while we do so, we never wish to ignore historical reality. For the sake of honesty and truth, we need to acknowledge the presence of very real flaws even in those God used in dramatic and far reaching ways.
One such example of this is the treatment of Fritz Erbe. Fritz did not embrace infant baptism and the terribly severe treatment he endured because of this, even in the same location where Luther translated the Bible into the German vernacular (the Wartburg Castle), reveals a sad truth that is often overlooked. Dr. James White explains (beginning at the 1:05:04 minute mark):