Reading nigger in Hick Finn is one thing, reading it in the works of the greatest Black American authors is another. As you progress up the cannon the use of negro, nigger an and colored all denote different levels of social standing and context in the works (they were fine reading negro and colored aloud btw). The words were carefully applied by gifted writers who were making keen observations on the experience of black Americans in their time. Which term a person was addressed by or self identified as could carry loads of subtext in the story.
And that's one of the best values of literature and teaching and assigning these uncomfortable books in classes at a young age. Literature has a power to teach that few other things do. It is a way to provide an experience for people that can't experience it. That suburban white boy is never going to understand living as a black man in a poor neighborhood, even if he lived there, in a way that a book written from that perspective can. It's extraordinary and one of the most incredible things human speech and language has achieved. I couldn't justify removing words that are vital to understanding what's happening. If someone can make the claim "this has the value of teaching these kids about racism and its horrors" how can they make the claim "but showing the language they face doesn't have value"?