Why is the ending of Huckleberry Finn controversial?

Could you elaborate on why the ending of Huckleberry Finn has sparked such controversy? Many argue that it contradicts the themes of freedom and individualism that run throughout the novel. Do you believe the ending undermines the overall message of the story, or does it serve a purpose in highlighting the complexities of societal norms and expectations? Additionally, how has the controversy surrounding the ending influenced the way the novel is taught and interpreted in classrooms today?