Lee Daniels is wrong - this is a movie, set in slavery times. That word, and words like it, were used all the time. This isn't necessarily supposed to be taken like a documentary, but definitely it's fair for the word to be used by slaves and slavemasters in a movie featuring slaves and slavemasters.
That said, the overall debate on the word still isn't really open as far as I'm concerned. People know who can/should and cannot/should not say this word. If you have to think about it for even a second, you probably shouldn't say it. If your reasoning for using it has anything to do with defying conventions suggesting you can't use it, you probably shouldn't say it. If you aren't ready to fight with/be possibly seriously injured by people for using it inappropriately, you probably shouldn't say it.
It's just not for you, and you should be okay with that. If you don't agree, just say it casually and stop caring about what might happen - take responsibility for it.