There’s a fine line between preserving something and understanding the historical significance, and excusing the flaws, be they racism, sexism, whatever, by saying it’s relative.
I get annoyed when, for instance, people write off American genocide because “they didn’t know any better” or “that was the times”. Just because someone doesn’t know better doesn’t make it not evil. In the same regard, a sexist statue from ancient Rome (or from 1922) is still sexist, even if the significance of that sexism is different and contextual.
And if anything, the use of language in Huck Finn is done in a way to insult racists.