Carson shares two attributes with Obama, other than race. One, he is prominent and considered a potential presidential candidate soley because of his race. A retired white doctor, no matter how prominent, would have elicted yawns from the media. A black conservative one however is news.
Two, he is unqualified to be president. Obviously, he's more qualified than Obama, having actually run something, but he has never held public office. Other than a few inspiring speeches, we know nothing about him. Don't forget all the heavy breathing for another admired black guy, Colin Powell. Can you imagine what a disaster that dolt would have been as president?
You want someone with a track record in public life, so we know what his principles are and how hard he will fight to advance them. I fully understand the desire to have a candidate who has some backbone and seems to stand for something, ie not Romney, and is not obviously crazy, ie not McCain, but that person should be a current or former governor or senator. They should be someone who has demonstrated an ability to win at least on the state level, ie not a representative. President of the United States is not a starter job.