I have to admit, I can sympathize with the fundies on this one, at least on the basis of appearances. If The Da Vinci Code were purported by the author to be a work of pure fiction, then all this would be a bit silly. I distinctly remember, however, the preface of the book talking about how the descriptions of the art and historical documents and whatnot are accurate, the implication being that Brown really is arguing that Jesus was a completely mundane nobleman type who ran off with some sweet piece o' social status named Mary Magdalene and they travelled the world together and had lots of nobleman type babies. Maybe I'm wrong on this, but that's how I interpreted the preface.
So, if the book is attacking the divinity of Christ, and thus the Incarnation, the Transfiguration, the Crucifixion, the Resurrection, the truth of Scripture (in any sense, literal or otherwise), and the legitimacy of the Church (Catholic or otherwise), and if Christian churches define the basis of their religion as a trinity of Christ, Church, and Bible, then isn't the book by definition an attack on Christianity? Furthermore, are Christians wrong in noting that there is a relative dearth of material from secular types attacking other religions, and thus are they wrong to feel singled out in the prevailing cultural atmosphere?
Even if you disagree, you have to admit that Hollywood coming off of its liberal onslaught in 2005 and making a movie about this book its big summer showcase looks bad.
All this is not to say I'm joining the fundie crusade against Hollywood or secularism or whatever-- I don't think an omnipotent God needs me to defend God-- I'm just saying that their feelings of being attacked are, at least prima facie, justified.