Ben Carson and the legitimacy of dissent
Interesting point about the Left projecting sins onto conservatives in the matter of Dr. Carson - both their own sins, and those they find necessary to impute to their opponents, in order to preserve their world-view.
A great deal of liberalism simply stops working if the legitimacy of dissent is accepted. To put it another way, as you've doubtless seen many times, liberals - all the way up to top national figures like Barack Obama - routinely assert that dissent from their policies with good will is impossible. Everyone who disagrees is a venal liar acting out of greed, racial hatred, contempt for the Little Guy, etc. Disagreement in good faith is not considered as even a remote possibility; average people who mistakenly believe they hold such dissent from liberal orthodoxy in good faith are merely the dupes of the shadowy, ruthless, well-financed forces Obama is always complaining about.
People of any ideological inclination are theoretically subject to this kind of paranoia, but it's become nearly universal and elemental among the modern Left. One reason is their belief in the absolute moral superiority of government power. Even when the collectivist State objectively fails, it receives boundless credit for its good intentions. Conversely, no one really "cares" about an issue until he supports the exercise of government power to "solve" it.
Besides the simmering racialism and tactical need to destroy someone like Ben Carson - the Left well understands the value of pre-emptive strikes when using weapons of mass contempt - he's a problem because he's making sound moral arguments against things the Left considers sacred, such as progressive taxation. The possibility of morally legitimate dissent, especially from a member of a demographic the Left believes it owns, cannot be allowed, or the never-ending struggle of righteous Big Government to protect us from sinister private-sector evil will come into question. This is also a factor in the Left's antipathy toward religion in general. You'll notice they're quite happy to bring religion back into the discussion when it can be used to build a moral case for government.
That's why one of the most brilliant up-from-nothing doctors in America is being treated as the dimwitted puppet of sinister racist interests by people who cannot match a tiny fraction of his accomplishments. He'd still be in trouble if he was just reading from spreadsheets and talking about the fiscal crisis in dry accounting terms, but the assaults on him are vicious because the idea that a good man of great intellect could reach his moral conclusions about government and liberty must be snuffed out.