I wrote this long post defending my point, and about halfway through, I realize it was mostly wrong. I think the screening off point is probably a better description of what's wrong with Pinker's analysis. Specifically, the higher rate of crime among blacks should be screened off from consideration by the fact that this particular black defendant was charged.

To elaborate on my earlier point, the presumption of innocence also serves to remind the juror that the propensity of the population to commit crimes is screened off by the fact that this particular person went through the arrest and prosecution screening processes in order to arrive in the position of defendant. In other words, a rationalist should not use less evidence to convict black defendants than required for white defendants because this is double counting the crime rate of blacks.