This would seem to tell you all you really need to know about Rodney Stark’s God’s Batallions: The Case for the Crusades:

Clearly this is not the politically correct version of the Crusades, and that is fine: there is little that was politically correct about the Crusades in the first place. The difficulty I have with Stark’s account is not that it is controversial and even confrontational, but that his conclusions are often grounded in outdated historical sources—many of the same sources responsible for creating the portrayal of backward, barbaric Muslims in the first place.

Stark concedes that his book is not based on his own exploration of the primary sources. He writes: “Many superb historians have devoted their careers to studying aspects of the Crusades. I am not one of them.” Instead, he describes himself a synthesizer of existing research. The curious thing is that much of the research he uses to refute the historical accounts of the past generation is itself over 30 years old. Does God’s Battalions, then, prove that the accounts of contemporary historians are wrong, or does it merely revisit and resurrect the scholarly accounts that gave rise to contemporary Crusades historiography in the first place?

If you’re writing as a popularizer or a synthesizer, you’re conceding that you don’t have first-hand expertise in the subject matter. All the more important, then, to rely on state-of-the-art scholarship. Unless, that is, your goal is to grind a particular ideological axe.