Carson's big mistake is that he assumes the foundation of what we call morals is a cognitive effort. It is an instinct bred into us by natural selection for good selective reasons.

If he read The Selfish Gene, or understood evolution, he should understand that the basis for what we call morals is in natural selection of optimal game theory solutions, effectively. The "tit-for-tat" strategy, or some variation thereof, is the optimal solution for the Iterative Prisoners Dilemma, for instance. Since that models a large class of social transactions, those with an instinctive "tit for tat" instinct would reproduce more often than those who don't, up to a point of equilibrium with free riders. Selection pressure would then tend to push better "free rider" detectors as well as free riders getting better at concealing it. It's your standard genetic arms race.

Now of course we aren't limited to pure instinct for given situations. We can cognitively apply our instinctive foundation to new situations and even override these instincts.

So when Carson says that Dawkins has no moral foundation and everything is preference, he is wrong. Dawkins has the same instinctive foundation as mostly everybody else. And violating these instincts isn't without consequence. We have the neurochemicals of guilt and the social punishments of those with free rider detectors. Doing away with God doesn't suddenly do away with these, nor does it change the game theory solutions that selection works on. These solutions will always be optimal for the types of social transactions we have. In that sense they are "moral" absolutes.