Well, I kept trying to think of a coherent argument to make about John Derbyshire's racist rant, but everything I thought of was either too obvious ("racism is bad, mmmkay!") or so beside-the-point that it risked distracting people from the badness of the racism. So instead of a single long post, I thought I'd list a few loosely connected thoughts I had in response to the rant.
1. Derbyshire really is racist, and his racism really is dumb.
Intelligent racists these days tend to defend their bigoted statements by prefacing them with a disclaimer that "What I say is only true on average," or "This is just a statistical tendency." Derbyshire does the same thing at the beginning of his rant. But then he goes on to make prescriptive statements about individuals based on those "statistical tendencies"! He goes from "On average, black people are more violent" to "If you see black people, you should avoid them."
This is a statistical and logical fallacy, as any researcher knows. Descending into nerdspeak for a moment, statistical significance is not the same thing as effect size. In plain English, this means that whether a person you see on the street is black is not a useful indicator of how likely they are to attack you. There are much better ways of predicting who is likely to be violent, just from looking at them.
For example, take a look at these two screenshots (the former from the movie Boyz n the Hood, the latter from the TV show Community):
If you're walking around and see people who look like the guys in Screenshot A, you might reasonably want to avoid them (though actually I wouldn't, but save that for later). Why? Not because they're black! Because they look poor, tough, and mean. Those would be good reasons to avoid someone who looked like Ice Cube looks in Screenshot A. Their blackness would be beside the point. It would not be an important consideration, on top of the other things you could already see. If they were Vietnamese, there would be absolutely no less reason to avoid avoid them.
Conversely, if you see some guys who look like the guy in Screenshot B, you would have no good reason to avoid them. Troy from Community looks like an even-tempered middle class guy - a guy who is highly unlikely to attack anybody. The fact that he's black makes no difference at all. If you go around avoiding guys who look like Donald Glover in Screenshot B, you aren't being prudent, you're just being an idiot...you're like one of those OCD kids who never steps on cracks in the sidewalk, except that instead of simply looking like a doofus, you're making people uncomfortable.
To put this another way: Suppose you see a bunch of rowdy-looking, tough-looking 18-year-old guys swaggering down the street in a poor neighborhood. Do you think to yourself, "Oh, if those guys were white, I'd go up and ask them for directions, but since they're black, and because I have this theory about ancient African evolution making black people more violent, I know they're likely to be violent, so I'll avoid them."??? No. No you do not. Because you are, hopefully, not an idiot.
So it's easy to see that the "statistical tendency" of black Americans to commit more violent crime should have no implications for behavior toward individuals. Violent people of any race are easy to spot. This directly contradicts Derbyshire's admonishment to avoid black people. If they follow their dad's racist advice, Derbyshire's kids are just going to look like idiots and be socially ostracized, without actually being any safer.
2. I actually find poor black people less scary than their white counterparts.
Here's my personal background. I grew up in College Station, Texas, which in the 80s was a highly conservative, mostly white town with a small, mostly poor black population. My neighborhood was next to the neighborhood where the poor black people lived, so I rode the same bus as them. There were a smaller number of white kids on our bus, mostly lower-middle-class Southern whites.
The black kids on my bus never once bothered or threatened me. They clearly had a culture that was very different from mine, including a very different dialect of English (which I eventually learned to understand). But they never tried to bully me, and never acted unfriendly toward me (they would always let me sit next to them, and usually would let me have the window seat so I could read a fantasy book or sleep).
The same was not true of the Southern white kids. They were also very culturally different from me (I was a nerdy Jewish kid with Northern parents and no Texas accent). While the black kids were on the bus, the Southern white kids would be sullen and silent, but as soon as the black kids got off, the white guys would start trying to bully me. They were definitely aggressive and targeted me, other non-Southern whites, and Asians.
I asked my mom why this was the case, and she shrugged and said something like "Maybe it's because the KKK hates black people and Jewish people!" I thought that sounded a little far-fetched (though the Southern white kids often spoke approvingly of the KKK when there were no black people around!). I came up with a different hypothesis: I was too different from the black kids for them to see me as a threat or competitor. People usually don't just attack strangers just out of pure sadism; they assert their dominance over competitors. To the black kids, I was just some kind of interesting oddity; to the Southern white kids, I was a white kid of a different tribe, and one who needed to be reminded of his place.
This pattern has repeated itself in other times and places. In California, in Japan, and now in Michigan, I've found that black people never want to fight me, but white people sometimes do. Although I generally avoid people who look tough, poor, and violent (see Thought #1), I sometimes break this rule for nonwhite people. Once or twice, I've gone up and started chatting with "gangster"-looking black dudes on the streets of Tokyo and Detroit, and they turned out to be pretty friendly. Now I'm not stupid - if I do that 1000 times I know I'm eventually likely to get mugged - but I wouldn't even try asking directions from a bunch of drunk rowdy-looking white guys walking down the street in Ann Arbor.
Who knows, maybe it was just the school bus that made me who I am.
3. I think Derbyshire-style racism really is holding back black people in America.
The disappearance of explicit racial discrimination in American public life has convinced a lot of people that racism is no longer holding back black people. I disagree.
An outsized percentage of black people in America are poor. Because of the cultural pathologies that stop American poor people from forming stable families (see Daniel Patrick Moynihan's 1965 report on poor blacks or Charles Murray's recent book on poor whites), this means that an outsized percentage of young black men are going to be violent. And given the prevalence of gun ownership in America, violence here is very dangerous.
This puts Americans in great danger of committing Derbyshire's Fallacy - of assuming that race is a good proxy for violence. Many white and Asian Americans share Derbyshire's fear of associating with black people. This means that white and Asian Americans are less likely to have black friends, which means that black people are often frozen out of networks of business and professional connections. That makes it harder for black entrepreneurs to embed themselves in existing white and Asian networks of customers, suppliers, and business partners. It means that black employees will have fewer white and Asian connections when they are looking for a job.
The separation of black networks from white networks will keep black people poor. And black people's poverty will keep causing people to indulge in Derbyshire's Fallacy. It's a stable equilibrium.
How do we break out of that equilibrium? I'm pessimistic, because I know how easy it is to assign race an outsized importance when making judgments of people. If someone cuts you off on the freeway, your first thought probably isn't "Oh, that incompetent driver!", it's "Oh, that old person!" or "Oh, that Hispanic person!" or "Oh, that woman!", etc. We humans are hard-wired for tribalism, not Bayesian rationality.
There are, however, some things we can do. One is to continue to admit lots of nonwhite immigrants. Asia has a lot of these. Just getting rid of the notion that white Americans are "the real America" should go a long way toward eliminating the deeper, more dangerous racism left over from the old Confederacy. When admitting immigrants from Africa, we should make sure to especially focus on high-skilled immigrants in fields like engineering, computer science, etc. There is no shortage of these, as the burgeoning numbers of Nigerian, Ghanaian, Ivorese, and Senegalese electrical engineers and software engineers at American universities demonstrates. It's hard to argue that black people are dumb when you need to ask their help on your semester project.
Also, we should just do sensible things like ending the drug war, breaking up concentrations of poverty in inner-city government housing projects, etc.
And finally, there's urban policy. America is caught between a suburban/exurban racially-segregated past that is no longer economically feasible, and a dense urban/suburban future that is being stymied by low funding for public transportation, and by zoning regulation (see Matt Yglesias). The faster we manage the transition to the new urban America, the sooner Americans will be forced to live around people of all races. When that happens, people will learn that it makes sense to identify dangerous people by their clothes and attitude and behavior, not by their race.