He should not have chosen such subtle source material. The civil rights movement in the 60's wasn't pretty to watch. The book knows that. The death, pain, illegal imprisonment and showboating that were a part of the civil rights conflict in Alabama are completely absent from the film. King was a great man, but he was most certainly a man - try shooting him like one.
Sex is an important tool of power in the book.
But not in the movie. Again this must be a function of the PG rating, but the character of Lucille loses a great deal of her powerful center as a result. She uses sex as a tool to get what she wants and has no regrets about doing so. This character trait is abandoned in the film and it weakens the character. The characters that are left out of the film are important.