I think he's just saying that not all rational evidence should be legal evidence. I don't think that he should be read according to LW conventions when he calls lower evidence standards for blacks a "rational policy". He doesn't mean to say that it would be rational to institute this policy (and yet somehow also morally abominable). He means that institutionalizing Bayesian epistemology in this way would be morally abominable (and hence not rational, as folks around here use the term).
lower evidence standards for blacks
It's already been pointed out that being a member of a group is evidence, so the evidence standards are identical. This is important because some evidence screens off other evidence.
The problem with our conversation is that Pinker's argument is so wrong, with so many errors sufficient to invalidate it, that we are having trouble inferring which sub-components of it he was right about. I encourage moving on from what he meant to what the right way to think is.
This thread is for discussing anything that doesn't seem to deserve its own post.
If the resulting discussion becomes impractical to continue here, it means the topic is a promising candidate for its own thread.