It was explained to me that it was an attempt for some in the black culture to "take back," that word in an attempt to declaw it by swapping out the -er for an -a and using it colloqually rather than insultingly. Other people in the black culture think that word shouldn't be used at all, hard R or not, because it is so historically disparaging. I tend to agree with the latter.
I always wondered why that word had such negative connotation over other pejoratives. I believe it was Maya Angelou who said, paraphrasing, "it's so hurtful because it was the last word people heard before the noose tightened around their neck."
Some dark stuff.