Nobody sane denies there is a legacy.
The differences of opinion are over what caused it, what perpetuates it and how to address it.
Accusing the right of dehumanising tactics is amusing, as stereotyping the right as, oh for instance, being chimps, isn't new.
Its jot about being sane, its about being informed. The problem is both sides tend to default to negative responses, mainly due to the negative emotions they elicit. That the left engages in language intolerance does not mean the right's efforts are validated, especially given historical context. The right certainly has the right to be offensive, but they don't have the right to not be criticized for it.