In the Bible, Jude has a fascinating passage concerning those who "speak evil of dignities" and "speak evil of those things which they know not". (Jude 1:8-10) When you couple these descriptions with the general counsel of Jesus to "Judge not, that ye be not judged," I think it is apparent that the worst thing about "evil-speaking history" or criticism of religious leaders is that generally it is undertaken and compiled in a spirit of belittling rather than understanding.
All of us are fallen and come short of the glory of God, so it isn't necessary to focus or dwell on the proof of that fact - particularly if all it accomplishes is to dull our appreciation for the wonderful things some have done. Does knowing Winston Churchill was a rude drunk make any difference in the grand scheme of things? Perhaps so, if it is used to point out his greatness despite his weakness and encourage greatness from us despite our weakness, but if it is used purely to denigrate him, of what use is it?