Even Carson as the GOP nominee would obliterate one of the most successful political narratives the left has ever had. They know this. Hence the hate for Carson.
The Democrats have plenty of reasons to hate Carson. 1) He is conservative. 2) He is black. It is the Democrats that are actually racists. Their only interest in blacks, women, latinos, etc. is as pawns to advance their political power. What is that called when you USE a sect of humans to improve yourself without regard to the personal effect of said fellow humans? Bigotry? Racism? Sexism? Slavery? Democrats have managed, through political correctness, to hoodwink their loyal subjects into volunteering to be dependent servants of their own masters. "What will you promise me next, Master? Then I will vote for you."