When did Dan Brown become so powerful?
It's not a matter of Dan Brown being powerful. He's just a hack writer who collects conspiracy theories and throws them together in novel form.
The issue here is that Christians are tired of constantly being bashed in novels, films, and other media. If Islam were bashed in this manner it would be considered bigotry and every film critic in America would already have given the film a negative review without ever having seen it. Not to mention that those involved with the film would have bounties on their heads.
But since Christianity is the only religion it's Politically Correct to treat in a negative manner, and since Christians don't decapitate people on live TV, we're the ones who get bashed all the time.
Imagine if you were a fan of a particular sport team. You and other such fans are well behaved and never riot or harm others. However, fans of a rival team riot all the time, and even kill opposing fans and players on occasion. They issue death threats, bomb threats to stadiums, actually plant bombs, etc.
Yet, you pick up a novel or turn on a movie, and quite often it's about a crazed fan of your team killing, raping, bombing people, engaging in grand conspiracies of various types. You never see these things being done by the fans who actually behave that way.
So you try to find out why. And the answer is that your team and your fellow fans are "out of vogue" with writers, actors, and directors, while the team whose fans really are violent is considered Politically Correct and thus can't be caricatured negatively without loss of Tinseltown social status. Besides, since those guys really are violent, it's dangerous to write a book or produce a film that portrays them as anything less than wonderful. It's much safer to pick on people who won't kill you.
Wouldn't you get tired of that after a while? Well, imagine how people feel when it's their very faith in God that's treated this way, not just their favorite sports franchise.