I just got around to reading the notorious article by John Derbyshire that led National Review to sever its ties with him. To do an extended critique of the piece would be to accord it more respect than it merits, but there's one line in it that serves as a kind of microcosm of the whole thing and sheds some light on the mind of Derbyshire.
The piece consists of advice Derbyshire has given his children for navigating a world featuring black people, and one of his tips is, "Avoid concentrations of blacks not all known to you personally."
So let me get this straight: If you see five black people that you know personally, and they're in conversation with a sixth black person whom you don't know, there's a danger that the sixth person will assault you or something? Don't you think that, actually, if those five people are decent people, chances are they're not hanging out with a thug--and certainly not with a thug who would assault a friend of theirs in their presence? Wouldn't Derbyshire apply that rule of inference to white people? Why wouldn't the rule hold for black people?
And of course, there's also the fact that, even if you knew none of the six people, there might be cues that could put your mind at ease. If, say, these six black people are well-dressed middle-aged men, you could make the same generalization you'd make about well-dressed middle-aged white men: they're not crackheads who need money for their next fix. Similarly, for both young black males and young white males, there are cues that correlate with danger and cues that are cause for reassurance.