I have seen a number of screeds condemning the Church wholesale for its many past crimes. I agree entirely that the Church has perpetrated many crimes: simony, the massacres, the burning of heretics, the accumulation of wealth, and so on. But I think that some people go too far, rejecting the Church as an entirely evil component of Western history.
This graph, for example, represents a lot of ignorance of Western history. The Church was not, as one book claims, responsible for the collapse of classical civilization. Many hypotheses have been proposed as partial explanations for that collapse, and the "guilty Church" hypothesis has to be at the bottom of a long list of ideas.
I suggest that three factors must be given due consideration in any discussion of the role that the Church played in Western history:
1. The Church's behavior at any given time must be evaluated within the cultural context of the times. For example, simony was merely the Church's own version of a practice that was common in the West. Indeed, the purchase of military offices was standard practice in many Western nations right up into the Napoleonic Wars.
2. The Church was a huge organization consisting of millions of participants spread over nearly two millennia. In any collection of human beings, there will be saints and sinners. There are some truly monstrous figures in Church history; there are also some genuine heroes. I am not excusing the Church for "a few bad apples"; I am instead demanding that the heroes deserve our consideration, too.
3. The Church made many contributions to the advance of Western civilization. It preserved much of the literature of classical civilization. Most of our historical records of the period from the collapse of classical civilization to the Renaissance were written by churchmen. Church thinkers advanced Western thought for centuries. Let us not minimize these important contributions.
Let's consider, for example, the famous confrontation between Galileo and the Church over Copernicanism. The high-school version of this confrontation is that the evil Church, determined to preserve the ancient ways, suppressed scientific progress by punishing Galileo and threatening him with death. The truth is much more complicated, much more interesting, and much less mythological in texture. Galileo engaged in some duplicitous behavior. He had many supporters within the Church, including Cardinal Bellarmine and Pope Paul V and Pope Urban VIII. Wikipedia has an excellent summary of what was a very complicated situation, although it leaves out some important antecedent details.
My intellectual curiosity has led me to explore many topics, and I have learned that it is impossible to understand Western history without a firm grasp of the role, both positive and negative, played by the Church. Along the way, I have learned much that illuminates other areas of interest.