The racial slurs are critical as Twain used them to indict the culture of the antebellum American South, and not to endorse its prejudices. When Huck Finn chooses "All right then, I'll go to Hell" by helping Jim, he goes against his ingrained social training as a white Southerner.

People who want to censor Twain misunderstand his message, either out of ignorance, or purposefully so as to take the sting out of Twain's social commentary and rewrite history.

Perhaps you can think of some works of literature set in India where characters utter analogous slurs, and the purpose of the author is to criticize the caste system?