Most DA's are elected. They have the same accountability, to the voters, that any other elected office has. Democracy does not shield us from "psychopaths" that are sometimes voted in to various elected offices. The solution is to vote them out. However, this solution is often disregarded, witness the long career of Ted Kennedy.
If in fact Nifonging is going on routinely, then the accountability of the ballot box is inadequate. Full stop.
The question before the house is whether nifonging is in fact common - and, if so, what mechanisms might change the incentives our nifongs face. Clearly Nifong himself faced the need to get elected in a venue in which the black vote was crucial, and that led to the malicious prosecution of three whites. And the same thing has definitely happened in reverse, especially historically but undoubtedly even today.
In cases when the black is the target, it's only too likely that the black has nowhere near the resources behind him that the Duke young men had behind them. And the black has the additional liability of belonging to a group which in fact is the source of a disproportionate fraction of our crime. So a black accused of a crime is a "Dog Bites Man" story; the Duke case was Man Bites Dog and that not only made it a juicy story but it raised the stakes. Nifong got his reelection, but he also got nationwide publicity that helped to bring him down.
It is an outrage if a prosecutor prosecutes with reference to politics at any time. Equally it is an outrage if the prosecutor refuses to prosecute with reference to politics, when the evidence would justify a conviction.