Examples: Huckleberry Finn edited to remove all instances of the N word, or the Mary Poppins books edited to remove the non-PC parts (specifically the "Bad Tuesday" chapter in the first book).
I don't think they should be edited. These books were products of their time, and of their authors' unique perspectives on life as it was lived and had been lived during their own lives. "Cleaning" or "sanitizing" these less attractive portions of beloved books does not help us achieve a post-racial or whatever society; IMO it is a step down the path to forgetting our own history. As George Santayana said, "Those who cannot remember the past are condemned to repeat it."
I think it's much more interesting and better if the books are left with their less-savory bits intact, and then highly productive discussions regarding those bits can ensue, especially with books for children.