The first and foremost reason is that having a black opponent will upset Barack Obama’s reelection strategy, which is to promiscuously play the race card against the Republican nominee: every time the GOP contender criticizes Obama, it can only be because he is raciiist. They can’t do that if Cain were the nominee. Or rather, they can and they will, but every time a white MSM reporter/Obama water carrier calls Herman Cain an anti-black racist, he look like an idiot.
The second, and more revealing, reason is that the existence of Herman Cain offends them - offends them personally. To many liberals, they measure their own virtue by how much they care about various designated victim groups, groups such as blacks, women, homosexuals, etc. So every time a member of one of these groups plays the victim card, it affirms their own saintliness: “See, look how bad society treats [member of victim group]. Good thing there are people like me to show compassion to the less fortunate.” And since compassion doesn’t require any effort on their part, the whole racket is very convenient.
But what if a member of a designated victim group refuses to play ball? Even worse, what if a victim group member tells the white liberals to stick their condescending paternalism where the sun don’t shine because it actually damages the interests of individual members of those groups? Now, a monkey wrench is thrown into the whole works. Their – their own personal – goodness is called into question. How dare they!
That’s what conservative like Herman Cain and Allen West do to white liberals. And for that matter, what Margaret Thatcher and Sarah Palin do to feminists. For our emotionally crippled elites, it's personal regarding people like Herman Cain.