Because I and others see this film as a symbol of Hollywood's disdain for people of the faith.
It's basically a boycott. My church and most others I know have been educating thier congregations about the message in this film and, apparently, many have chosen not to see it.
Talking it up in this board and others is a way of promoting the boycott.
How much of the poor box office is due to the boycott and how much is due to the crappiness of the film, I don't know.
Well, Brokeback Mountain was a smash hit, and Fahrenheit 9/11 and An Inconvenient Truth are 2 of the highest grossing documentaries of all time.
They will also reward any liberal minded film nicely at the Oscars, and snub anything that goes against their worldview.
None of this will change from any boycott, and with foreign ticket sales, DVD sales, syndication rights, and merchandising, the film will most likely make a profit.
I think your energies would be better spent elsewhere, not to mention the fact that lobbying people to avoid a movie you haven't seen yourself can be perceived as tactless and arrogant.