Christian Historical Revisionism
Do any serious reading on the medieval and early modern period in European history and it's guaranteed that sooner or later you'll run into someone (usually many someones) making the argument that the so-called "Dark Ages" really weren't as dark as all that, and that the significance of the Renaissance is overstated. My own assessment of such claims is that they're all a load of bunk, and the motivations of those who make them are usually quite transparent.
To be sure, there are any number of historians looking to make their mark in a well-dredged field by putting forward "shocking" theses, a la Niall Ferguson with his "The Pity of War", but by far the biggest propagators of revisionist "history" (or outright lies, to be frank) are those who seek to defend Christianity, with the Catholic apologists front and center in this fraudulent initiative. The motive for such mendacious scholarship ought to be obvious: by arguing that the Dark Ages weren't all that bad, one can try to make the consequences of a world dominated by priests seem a less ugly place than it actually was, the better to keep independent-minded members of the flock from straying.
The shameful truth is that Petrarch was right when he called the era between the fall of Rome and the renascimento an age of darkness; when knowledge was a monopoly of the priests*, ignorance, superstition, pestilence, famine, filth and intolerance were the order of the day, and the lot of the average European peasant was one that would not have been envied by his classical counterparts. It is true that there was the odd blossoming of learning during the fallow period in question, but not one of these was able to sustain itself beyond a generation or two before being overwhelmed by the ignorance that was ubiquitous in those times. Only with the beginning of the fraying of priestly influence in the Italian city states did Europe begin to enjoy a lasting upswing in human curiousity and avidity for learning, a rising tide that has gone hand in hand with the weakening of the priestly caste, right on to this very day. The church was no repository of classical light, whatever its defenders might wish to claim, but its extinguisher, and the ascendancy of the West owes a great deal more to the Islamic civilizations than it does to anything undertaken by the agents of the Bishops of Rome.
*And a shaky one at that, with few possessing a deep enough knowledge of classical Latin or Greek to do anything more than rote copying and recitation of ancient formulas and texts - much in the same manner many Muslims do with the Quran in our own time. It's laughable to think that despite the Catholic Church's claims to have acted as some sort of preserver of knowledge, study of biblical Hebrew and Aramaic amongst the priesthood was virtually unknown until the 16th century.
PS: Here's an article that ought to prove difficult for church apologists to swallow, indicating as it does that the picture of the greedy, gluttonous monk was a well-founded one.