Akeyata, regarding your points:
Point 1: Yes, it's fiction. But since when did being fiction make something inoffensive? So we can belittle any group, person or idea, and as long as we do it in a fiction format, no one can be offended?
But more importantly, did you read the review, or are you just assuming that everyone who dislikes the movie dislikes it for the same reasons? The review specifically states that the reviewers were "bordering on getting offended" "until Hanks delivered a monolgue that assuaged some of our fears." In other words, they weren't offended, so your first point is moot. (Incidentally, did you read the line in last paragraph that says: "So in the end, it's not a matter of being offended. It's not worth getting offended over."?)
Point 2: I won't try to defend another writer's word choice, but when no other academic religious symbologists back up Brown's ideas, it's hard to believe that Langdon is a Harvard Professor. Most of his symbology and history comes from conspiracy nut books, rather than art historians. I think that fits the phrase "cockamamie".
Point 3: I have no complaints with this point.
Point 4: I agree that the book was not meant to be an adventure story, but the movie is marketed that way, and I think that's its real downfall. They don't market it as a movie about ideas and history lectures -- they market it as a great conspiracy thriller, with car chases and fight scenes. If the movie doesn't do what the ads say it will, can you blame reviewers for thinking the movie failed?
Point 5: You say: "the only reason I can see is that this movie offends the unthinking christian." Way to jump to crazy conclusions. I can see why half-arsed history and manipulated facts appeal to you so much.
Point 6: I admit to having no knowledge of ancient grail mythology. However, you say that the movie might be requiring us to do our homework. Considering that every time anyone researches any of Brown's "facts", they come up with a whole lot of smoke and mirrors, I don't think Brown really wants us to do any homework. On the contrary, he wants us to swallow all of his bull, embrace his anti-establishment conspiracies, and then use pseudo-intellectualism to accuse skeptics of being "unthinking Christians". But maybe that's just me.