Vernon Tyson is a TEACHER??
How could you possibly remove Vernon's faith and job from this film? His stance against the white "Christians" of the late sixties and early seventies are the most compelling parts of the book. His faith sheds light on his reasons for being involved in the civil rights movements. His job as a preacher put him in a particularly vulnerable position.
Can't people of any faith, or no faith, admire a man who acts on his convictions to serve others despite the fact that he might lose his livelihood? Why would they remove that?
Because they are cowards. If this became known as a "Christian" movie, just because it is about a Christian, they are afraid people will stay away.
Don't you just love Hollywood?
My guess is in their pursuit of a mass (e.g. "beyond Christian") audience, they will lose the audience who really might have rallied around this film, and it might as well go straight to video.