Look, we have people on this very thread (e.g., maine-iac7) who consider Brown's version of history factual. Unfortunately, there are millions more people out there like maine-iac7. Whether it's out of ignorance, paranoia or wishful thinking, these folks believe in the "truth" behind Brown's book.
I agree with your assessment, but the motivation of the Da Vinci apologists go beyond mere ignorance, paranoia or wishful thinking. They are driven by a deep-rooted, pathological anti-Catholicism. Brown fuels their hateful emotions, not their intellects.