While the racial language is the primary reason for Huck Finn being banned, there are several other causes for the controversy that the book has caused. The novel was first published in England because Twain knew that American readers, particularly the American South, would not appreciate his harsh criticism of the culture and beliefs that were associated with the region at that time. The novel was published several years after the Civil War, and the wounds and bitterness between the North and South had not dissipated.
Secondly, Twain's portrayal of a precocious boy as the novel's savvy narrator and protagonist offended those who believed that good writers do not promote poor grammar and smart-mouthed children. While, of course, these elements are part of Twain's satire, many readers miss the satire and see the novel as a poor example of how children should act and talk.
Finally, modern readers still struggle with Twain's portrayal of Jim as simple and unintelligent. While some critics argue that Twain's motivation in his characterization of Jim was to demonstrate Jim's pure conscience despite his lack of formal education, Jim still comes across as a man who is to be pitied. I have to admit that it is always difficult to teach this aspect of the novel, because many of my students see Twain's portrayal of Jim as his true view of African-Americans from that time period. It is difficult to know what Twain's real motivation was in this area; so readers have to make their own interpretation of Jim's characterization.
The major objection to Huck Finn is its use of what we would now call racially insensitive language.
In the book, Mark Twain uses the word "nigger" over and over. This word, of course, is no longer acceptable for use by people who are not themselves African American. Since Twain was white, his use of the word is seen as racist.
People often fear that schoolkids who are exposed to the book will be harmed by the use of this racist language and by its other manifestations of racism (Jim is often treated as being pretty simple-minded and superstitious). They fear that black children will have their self-image lowered and that non-black children will be encouraged to hold racist attitudes.
The Adventures of Huckleberry Finn is considered objectionable for several reasons, but I believe it is mostly due to the amount of racial slurs that occur in the novel. The characters freely use the "n" word, a word now considered taboo, although that word was commonly used in day-to-day language during the time period in which the novel takes place. I also remember reading that because Huck goes against the rules and laws of society( even though we now know those same rules to be ridiculous), it could potentially have a negative influence on younger readers, allowing them to believe it is ok to go against social laws and regulations. I would say, though, that main reason why it is banned is due to the language.
When Mark Twain wrote The Adventures of Huckleberry Finn racism was open and very dominant in the South. Initially the story was not received well by his contemporaries not because of racial slurs. Instead the population was not thrilled to read a book in which a pubescent white male and a slave develop a friendship and relationship. Of course there were many people who just enjoyed the adventure of the story.
However, moving forward society saw a significant change after the Civil Rights Movement. The language used in the story was no longer acceptable and the characters were viewed as a degrading example of African Americans. The book was no longer politically correct. In 1957 the NAACP declared the book racist and belittling. It was removed from many school libraries as being a work that was inappropriate for children. There was a particular concern that the character Jim was a racist stereotype.
It is interesting that the vocabulary in the story is found to be offensive considering the way language is frequently used in today's text. Twain was trying to demonstrate to others the behavior and interactions of people in the south following the Civil War. That the book caused conflict is favorable in that it helped to make more people aware that it was not tolerable to stereotype people and use degrading language towards race.