There is a lot of nuance to this, but I suspect I know where DrDeth is coming from here. Maybe I am far too generous but here is what I think…
With Huckleberry Finn, the term is being used in a racist way. But not in a hateful way. Finn is good friends with Jim and I never got the feeling that there was any ill-intent behind it. But the term itself is absolutely, completely racist. It’s boiling down his entire identity by race by making it part of his name.
As for the second one, if he’s saying that Blazing Saddles as a film was not trying to be racist and hateful, and instead was trying to shine a spotlight on racism to mock it and subvert it, I agree. But the term was absolutely used in a racist way in the film. Racism was a huge part of that film; the core theme in fact, as Bart struggled to get the town’s residents to accept the authority of a Black person enforcing the law. Some period-appropriate language was used to express that racism, so I don’t feel its usage in the film was racist, but clearly the language itself was racist. It was supposed to be, that’s the point.