It fits every tired stereotype out there; and we can do much better than that
That, and it hurts the overall conservative message. To be clear, I think it's legitimate to talk about many of the issues that seem to attract such comments (e.g., black crime rates, black-on-white crime, black academic performance, black culture, etc.) but it undermines any legitimate points that might be made about those things to talk about them like a stereotypical racist. It turns black conservatives off. It turns plenty of whites off, too. And I've been told by more than one black that the reason they don't and won't vote Republican is because racists feel too comfortably at home on the right. So when people ask, "Why do black and Hispanic conservatives vote for Democrats?" the answer is that the belief that Republicans and the right are racist is so poisonous to the "brand" that those groups want nothing to do with Republicans or the right. That's sad, bad, and counter-productive.