"Christianity hasn't collapsed. In fact, some people seeing it have said their faith is even stronger."
I find a lot of people (including myself at one point) are just looking for an excuse not to believe. The rehashing of this forgotten heresy provides them a new source of excuses.
You know what? The people who love this film and the book are the same people who think that the Trilateral Commission is secretly plotting to take over the world. The belief in conspiracy, not matter how fanciful, is quite alive in America, to wit: Who killed president Kennedy?; We never landed on the moon...it was all done in a sound studio somewhere; The Mason are going to takeover America, etc.
Even if it were true about what the books says about Christ, how many ka-zillion people would have to keep there yaps shut for centuries to prevent the truth from leaking out?
And as for the people seeing the film and then asserting that it somehow made their faith stronger, well, that makes as much sense as blaming rain on wet streets. If this film strengthens your faith, you probably had very little faith to begin with.
Alas, the story is, at last, just a story made up to look real.
It's a crappy book and I'm not wasting $6.00 and 2 hours of my life on the movie, but with all due respect, those looking for an "excuse" to lose faith will find it in Spongebob Squarepants if not the Davinci Code.
Frankly, that's not your concern, IMO. Your job is to carry out the great commission, not to be the heresy police.