Both "The Adventures of Huckleberry Finn" and "To Kill a Mockingbird" use period-accurate racist language and stereotypes. However, both also offer an excellent vehicle for discussing racism and slavery. (Not to mention, in Huck Finn's case, alcoholism and family violence also are themes).
Most importantly, both tales facilitate a conversation about how one's choices and thoughts are influenced by the conventions of the society one exists within and the difficult necessity of challenging those conventions when they are unjust.
Denying students the opportunity to read these works in a structured classroom environment because they are "uncomfortable" misses the point. The students are supposed to be uncomfortable. Today's high school students live in a world fraught with racial tension. The real world inevitably will place our students (especially, sadly, our students of color) in situations where race will be an uncomfortable but unavoidable conversation topic.
We should not deny them the opportunity to have uncomfortable critical dialogue about these issues in a structured, teacher-led environment simply because it may be "uncomfortable."
Let's place a bit more faith in the ability of our teachers to impart these difficult lessons - and in our students ability to engage with them.