Although the potential for abuse is there, prosecutors do not have the "right" to abuse their power, and in fact are subject to discipline--including disbarment or imprisonment--if they do.
Prosecutors are officers of the state or federal government, dependent upon the jurisdiction under which they operate. They take an oath to uphold the Constitution of the United States, and the constitution of their specifrc jurisdictions. Their power includes the power to supoena witnesses and present informations or indictments to Grand Juries. Charges are then brought ONLY if the Grand Jury sees fit to indict. It is ludicrous to assume that a prosecutor could make decisions on charges based on race or ethnicity under our present system of safeguards. He would be challenged by defense counsel almost immediately, and subject to severe sanction if he did so. Every defendant is entitled to the right of counsel, and any hint of prosecutorial misconduct would be immediately challenged. Prosecutors do NOT have the authority or right to withhold from defendants or their counsel any information which might be favorable to the defendant; nor can they issue indictments with abandon, as each action he takes is subject to review by the presiding judge.
In short, the Prosecutor is nothing more than counsel for the State, or the People. There is a tendency, because of movies, TV, etc. to picture all prosecutors as bad guys out to get the little person. This is not true. Most prosecutors are honest and trustworthy. There are no more corrupt prosecutors than there are corrupt defense attorneys. Of course everyone has heard stories of crooked prosectors; but then everyone has heard stories of plane crashes. Precious few people won't fly because of that.
One of the powers that prosecutors have when pursuing a case has to do with what charges will be brought against a given defendant. A prosecutor may choose from a range of crimes that might be charged against the defendant. This discretion allows for (in some people's minds) abuse.
A prosecutor can, for example, choose to bring more serious charges against one defendant and less serious charges against another. These decisions may be made for legitimate reasons, but it is always possible that they could be made for corrupt reasons or for reasons like race or ethnicity. Because prosecutors have so much discretion as to whether to bring charges and what charges to bring, they have the ability to abuse their power.