Awhile back, I posted about a speech given by WMU's own Paul Maier about The DaVinci Code. I recently learned that the blog of John DePoe contains a link to an audio recording of the speech. It also has a summary of the talk that was handed out there.
Maier's talk convincingly deals with the "it's just fiction" argument. He points out that fictionalizing the foreground (the story) is acceptable, while fictionalizing the background is not. Dan Brown explicitly claims that this background information is factual on the first page of his book.
In addition to what he says, I would point out that fictional works such as novels, television shows, and movies have a significant cultural impact. This is because so many people spend so much time consuming them, and because people may not realize the messages that such works are sending. Thus straightforward nonfiction works may be less likely to influence people because they will be more on guard.
If you went to the Students for Like event at the same time and wonder what you missed, you should check it out.
Here's what Terry Jeffrey has to say about the movie.