The problem that I have with The Da Vinci Code is that it is confusing a lot of Christians who aren't well grounded in their faith. I have heard much nonsense coming from relatives who don't know early church history or much theology. The book is fiction, but it is hurting the faith of many Christians. I read the book and found it to be a poorly written thriller based on complete garbage.
I also studied art history in college and know that much of what Dan Brown writes about Da Vinci's paintings to be false. It doesn't take much research to uncover the truth.
If a book of fiction can hurt their faith then it was weak to begin with.