Brother, you have just described the study of history as a whole. I'd almost venture to say that nothing can be easily distilled into simple categories, but I cannot say that with certainty. Even issues that seem black and white have layers of complexity that makes the discussion a whole lot less simple than "Obviously <statement>." I went to the British Museum on Monday, and one thing that strikes me is how we often tend to think of historical events in terms of abstraction. "The Ancient Romans." "The Holocaust." "World War II." "The English Civil War."And that's the thing... the study of the Crusades is a huge, complex and nuanced thing...
Very rarely do we associate the events with the people and events behind them and when we do, it's often skewed. We look at the Nazis and see the faceless stormtroopers marching against the forces of "good" (Please bear with me here, these quotes are meant to indicate that there is a discussion to be had, and the discussion could take days). But do we think about how many Germans signed up for the War Effort because they thought they were defending their country? That, for better or worse, their intentions were roughly (Again, bear with the generalization here) the same as the soldiers on any other side? The situation of the Weimar Republic is barely covered in school (Well, it was for me, maybe you youngsters are getting a more comprehensive history class these days). The circumstances leading to the Nazi's rise to power are glossed over. Because of this, I know people (Thankfully not many...) who still think that Germans have secret Nazi tendencies (And those Neo-Nazi movements don't help matters...).
I guess my point is, the moment you try to summarize history into a single statement or view, you lose something. This is not always bad or inappropriate (Because no book can ever show the full picture), but it's farcical to say "All Germans were Nazis" or "The Crusades were about Christians killing wantonly" and pass that off as a good historical argument. Please do not misunderstand me when I say that Germany from 1932-1945 is a very misunderstood country. I am not trying to imply that the Holocaust was justified. I just think hasty conclusions about that period do more harm than good. To apply a wide label to such a large swath of history is not something to be done lightly.
Anyway, tangent, but point being: Rarely, if ever, is history clear cut. A wise man seeks many views to construct what likely happened. A fool accepts what fits with his beliefs and agendas. The lazy just accepts what they heard first.