Why are Christians so worked up about "The Da Vinci Code"?

...After all, don't they understand that it's just a novel (or just a movie)? These are common questions in response to Christian reactions to "The Da Vinci Code", and they are understandable questions. In answer to these questions, I would say that the problem is that many people who read this novel are in fact believing its outlandish historical claims, as evidenced by this recent article from the London Telegraph newspaper. Here are some relevant (and somewhat disconcerting) quotes from the article:

Two thirds of Britons who have read Dan Brown's thriller believe that Jesus fathered a child with Mary Magdalene, a claim rejected as baseless by historians and Bible scholars.

Those who have read it are also four times as likely to think that the conservative Roman Catholic organisation Opus Dei, whose members include the Cabinet minister Ruth Kelly, is a murderous sect.

Seventeen per cent of readers are convinced that the lay group, whose founder was canonised by the late Pope John Paul II, has ordered or carried out a murder, compared with four per cent of those who have not read the book.

The poll has shocked Church leaders who have mounted a massive campaign to debunk The Da Vinci Code in advance of the release of the Hollywood film version this week. The findings suggest that the book has significantly shifted attitudes towards traditional Christianity and will fuel fears that people increasingly prefer to believe in conspiracy theories that taint the Church rather than historical evidence.

Of course, I think that these numbers say more about widespread historical illiteracy, inherent biases toward Christianity and the Catholic Church, and a general willingness to believe in conspiracy theories, than they say about "The Da Vinci Code" itself. But still, these numbers give a very good indication as to why many serious Christians are not willing to ignore the impact of "The Da Vinci Code" based on the fact that it's "just fiction".