I remember learning about cultural relativism in a sociology course in college; the idea that we should judge a culture on it's own terms and not on our own. I think that's exactly what we should do in the case of old novels. I like historical novels and one of the things I want from them is that they be true to their times.
Mark Twain made liberal use of the N word in his novels. And I just pretended not to type it and instead typed "the N word". Does that make Mark Twain a racist or does it make me a wimp and a coward? Actually there's good reason to think Mark Twain wasn't much of a racist so where does that leave me?
A writer naturally includes the attitudes of their time and by reading their books we learn something about their time and it's pretty good practice at being open minded and that's a good thing.
If we blind ourselves to the world that used to be then we're cutting off a major source of understanding of the world today. And who are we to say we're better now than they were then? Watch the news before you answer that.
Barry