Here's an old interview about The da Vinci Code.
Q: What are the most important assertions about Christian origins that author Dan Brown makes in this novel? What seems to be disturbing people the most?
Welborn: Brown makes several assertions, none of which would be taken seriously by real, as opposed to fictional scholars.
The basis of the book is that Jesus, a moral teacher of wisdom, was intent on reintroducing the notion of the "sacred feminine" back into human consciousness and experience. He drew followers, and was married to Mary Magdalene, whom he designated as the leader of his movement.
This was opposed by another party -- the "Peter party" -- which worked to suppress the truth, which was ultimately achieved through the actions of Emperor Constantine who "divinized" Jesus at the Council of Nicaea in 325.
It is this suggestion that the Christian Church has been engaged in a destructive cover-up of the truth that has disturbed readers, as well as the idea -- propped up by Brown's assertions that "historians believe" -- that Jesus was not experienced as divine by his earliest followers.