Mankiw's excuse is lame. The problem is he's not a real economist anymore; he's a "market fundamentalist." He's relying on his defenders to argue that his critics are economic illiterates.

My textbook uses a smiliar dishonest rhetorical strategy. I don't have it here with me, but on p.x, it says people who worry about the trade deficit--and concomitant job loss--are mercantilists (and therefore idiots). On a later page it explains the Heckscher-Ohlin Theory as demonstrating that trade between capital-abundant and labor-abundant economies causes a permanent decline in income to workers. In that particular passage, no qualification is given--the authors might reasonably have paused to explain that the picture is more complicated than that, that the H-O Theory is not borne out by empirical analysis, or something. But they do not address the matter; the conclusions in Chapter 5 (both passages are there) are both triumphalist about free trade and pessimistic about its effect on workers.

PS: The above is not intended to make an argument about free trade. It's an argument about rhetoric and consistancy.

As an excuse, yes it's lame. But as an observation it's totally on point. The more I learn, the more I recognize how many "economic" decisions are being made on the basis of anecdotes.