Fair question! My girlfriend tends to be angry with the stumbling efforts of new media to adopt language that does not dehumanize or denigrate Native culture.
However, she would understand how a particular setting demands that the characters be mostly limited to the ideas to which they would be predisposed.
It could be helpful to include an author's sidenote about your feelings and intentions when writing.
Personally, I think your racist characters can act racist without representing the artist. Censoring this (ugly) part of history affects the integrity of your setting, and the potential for conflict or character development.
Colonial attitudes towards "civilizing the uncivilized" were so pervasive that they still affect territorial politics to this day, among other things.