I think the most convincing thing in Dalliard's critique is the section headed "Shalizi's second error" (the "first error" I think is simply a misreading of Shalizi; the "third error" is part misreading and part just Dalliard and Shalizi being interested in different things). Here, Dalliard says that Shalizi claims the only evidence offered for "g" is (in effect) the pattern of correlation between different test scores, whereas (according to Dalliard) advocates of "g" actually offer a whole lot of stronger evidence: confirmatory (as opposed to exploratory) factor analyses, various genetic investigations, etc.

I don't know enough about any of that stuff to evaluate Dalliard's claims against Shalizi's, though on the face of it it looks as if Shalizi has made a sweeping negative claim that on its face simply doesn't fit the facts -- it would be Shalizi's job to show that the arguments Dalliard points at don't actually support belief in "g", not Dalliard's to show that they do. If anyone reading this is an expert in any of the relevant fields, I would be very interested in their opinion.