(For instance, in Vaara's perfect universe, education programs in Africa can actually convince the people there to stop engaging in sexual behaviors which are at risk for spreading HIV. In the real world, on the other hand, such programs aren't practical because of other issues like wars and revolutions and incompetent governments.)
This is the textual equivalent of saying "look out behind you!" and running off when you get in trouble. Other then the fantastically unproven assertions involved in that last sentence, it shows that the "perfect is the enemy of the good" email that prompted this entry still permeates his blog in general and that he seems to feel the need to pull it out whenever he gets contradicted. He's still saying the equivalent of "nothing can work, we shouldn't even bother" even as he denies it, and attempts to misdirect criticism of that stance. Vaara still had a point.
This also enters into the rest of the entry, which talks about vouchers, school choice, and the (seemingly non-controversial) idea that some kids are just naturally kind of dim. Which is true, so far as it goes, but what is in question (and which goes begging in Den Beste's entry) is why this happens to be the case, and whether someone can do anything about it. Those kids who are "just plain stupid" could have ended up there because their education happened to be somewhat substandard, or because they have a specific learning disability that, when overcome, would show that they are actually pretty damned bright. (One of my best friends is dyslexic, which up until very recently would be classed as "a dim kid". She's brilliant.)
This is, in fact, the main argument against school vouchers that has always made sense to me... public schools are a "default" version, and private schools can exclude problem students, so private schools are going to be able to leave the public schools with the problem kids, reap the rewards of higher test scores and the increased enrolment that that provides, all while public schools have their funding removed and in a desperate attempt to rectify what cannot be rectified start cutting special education courses. Then, of course, my brilliant friend is called an idiot because she doesn't read the same way everybody else does, thinks she's an idiot because she hasn't the faintest clue that her problem is dyslexia, and "shuts off her brain", so to speak, because the assumption breeds the reality.
Does this mean that Den Beste doesn't have a point about the difference in potential between different students? No, of course some students are going to be smarter than others. Unless he can pull out much better evidence as to why this happens to be the case and why we're helpless to do anything about it (which seems to be a common thread in his entries- a curious attitude for someone who admires engineering so much), I'm not buying that it's a justification for school vouchers or anything much at all, in fact.
Like the unspoken yet still obvious assertion that governmental intransigence is so ingrained and unstoppable in Africa that we should just let them all die, the idea that we can't do anything for the dumb kids is one which is most assuredly not self-evident.