First of all, let me say that this was a documentary and therefore did not appear to be scripted. People were interviewed and Rev. Al Sharpton was one of the people interviewed in the movie, and his comments appear to be candid.
He was talking about how the black hair industry - which apparently is HUGE business - is owned/controlled mostly by whites and asians. And what he said was something to the effect of "If blacks can't take control of an industry that caters to them and only them, that's economic retardation." I took that to be disparaging, as in "financial stupidity."
Obviously there are contexts that the R word could be used in that are not disparaging and are not used to imply stupidity or disability. Fire retardant comes to mind. Not an insult. But what the good Rev said in the movie? Disparaging.
But again, it really just made me see him as an ignorant, classless person.