The author calls a spade a spade in ways that no politician ever would (if they knew the mic was on, that is)--voters are not just rationally ignorant, they are irrationally daft. And that includes you.
In precis: rational ignorance is not the cause of democratic folly, because via the wisdom of crowds, the smartest non-ignorant voter on every issue would prevail over the randomised noise, and the result would be policymaking at its finest. Instead, the errors are not random, but reflect the insidious working of Caplan's four main biases that voters have: 1) the market does not know best all that often, 2) foreigners are foes, 3) jobs are better than efficiency and 4) yesterday was better than today. Apparently these systematic biases previal because they feel good, and the return of good feeling is demanded by folks, so they supply the biases to get it. From another ten miles high, this actually all seems optimal (the people get what they want), but only in the same way as belief in Santa or faith healing are similarly demanded because they feel good to the mistaken.
And it's less innocuous than that too (as may be the faith-healing market)--if special interest groups (those poised to reap concentrated gains) can exploit the rationally not-bothered public (they pay diffuse costs), then they sure can do a job on the irrationally wrong public. Or so it would seem. Mancur Olson's thesis on collective action (renamed "classical public choice") gets an airing for this important reason.
What's the solution? It would seem that some of it is to let the market decide more often, and some of it is perhaps more devolution of policy to arms-length technocrats. So Churchill's proclamation that democracy is the "worst" form of government "except for all the others" seems to get the response: "Not always". And of course, democratic societies already know this to be true, since they have independent judiciaries and monetary authorities. However, this reviewer did not get to sense an abundamce of solutions. And at times, she wondered if the text was edging towards rule by Plato's philosopher kings (except that they would more likely be economist kings).
In that regard, it is possible to run away with the idea that the author is merely lamenting the failure of electorates to choose policies that he approves of. Non-economists would be quite likely to get rather irritated by chapter three, which had a persistent tendency to give this reviewer the impression that if she wasn't one, then by default her views were less correct. She suspects that this charge is going to seriously limit the penetration of Caplan's thesis in popular assessment, even if she can get over it herself. But in doing this, Caplan appears to trip himself up a little, since the rest of the text is noticably dotted with pockets of defence of dismal scientists against the foes he apparently imagines are already banging at the door. More likely--and this is unfortunate--they stopped reading some time ago.
having just grappled with 700 pages of 17th century English prose ("Liberty or Freedome signifieth properly the absence of Opposition (by Opposition, I mean externall impediments to motion); and may be applyed no lesse to Irrationall and Inanimate creatures, than to Rationall") and sort-of lost. 
.
