This is a topic I feel very, very strongly about, even when it is very small instances of it. I don't believe in whitewashing our history in any circumstances, there's simply no excuse for it. Even small instances such as removing the word nigger from Huck Finn upset me. If you are teaching people that are still uncomfortable with its use confronting that directly is of far more importance than anything else you could get out of the work. First of all, because Twain wanted a level of discomfort and tension between Huck's perspective and the use of the word and that entire layer is removed by the word change (I remember studying this in my American literature class in college, use of language was important). Secondly, because you have to deal with the history you have, not the history you want, and it's critically important that people learn to deal with the reality of the world they live in and come to terms with that. Also, they need to learn to deal with historical time periods in that period's terms, not in ours. I can think of few more corrosive things to teach than that you can simply change the facts to suit your prejudices when the facts are inconvenient.
Of course, if this was a book aimed at grade school kids my opinion would be less strong, these ideas wouldn't be age appropriate. But if people can't deal with original texts from 130 years ago on their own terms by high school how the hell are they supposed to deal with any aspect of the world that doesn't conform precisely with their own worldview? Dealing with the past or other cultures without reading your own values into them is one of the most important things anyone needs to learn to deal with our world. This sort of action just lends legitimacy to historical revisionism and shameless anachronisms and there is simply no valid defense for. If a person can't deal with this and finds it too offensive they're simply unable to deal with reality on any level capable of meaningfully contributing to our social discourse. If it offends you great, that's a wonderful reaction to have and what the author intended, use this as a bridge to learning about the culture of the time and its differences from our own. There's really nothing that can be added to our social and cultural discourse by a point of view so easily offended that it demands historical revisionism to obscure the culture of another era and our own historical legacy.
Jumping off of this, I think a real contribution could be made to our school system by requiring that high schools assign several books a year from cultural and historical perspectives that will be offensive to modern readers. Getting offended is an essential part of the learning process in coming to terms with just how much attitudes change across time and space. It's healthy, and should be encouraged.