In the book, Paul does everything he can to avoid the jihad he sees coming, because jihad = religious fanaticism = bad. A crusade is also religious fanaticism and is also bad, but portraying the term “crusade” as an evil to be avoided could be a good thing for an American audience. Crusades are a part of Christian culture, and if you’re going to write religious criticism there’s less of a risk of it being misinterpreted if you use the audience’s dominant religion as an example. If you criticize religious fanaticism using the religion of the Other, it’s easy to interpret that as nothing more than “Other bad.”

Plus, we’re almost guaranteed to get some Christian chuds throwing a fit over it, especially with the rise of right-wing “crusade” imagery. That’s always good for a laugh.