If you ask me, the catholic church reacting so negatively to the book and movie only reinforces the idea that they are covering something up. I personally dont think it holds much merit, but I also dont think we know the whole story about Jesus. The bible leaves out many chapters in his life.
Another thing that is a little fishy but has never influenced my faith in either directions is how some groups think that Mary remained a virgin. What man marrys a woman and doesnt get any.. ever? The bible clearly says that Jesus had brothers. So in a way, I could see how if the catholics knew that jesus had a child or had sex they would try their damnedest to cover it up. The thing that puzzles me is why? Sex within the marital bond is not a sin.