somewhere around Marxism in politics.

Shalizi states at least part of his position as follows:

"Market socialism" is a current of ideas [...] for how to make extensive use of markets without thereby creating gross economic and political inequality. [...] On the other hand, modern states are powerful enough as things stand; to turn the economy wholly over to them is a bad idea. To combine markets with socialism seems like an elegant and feasible solution, at least technically, and it's one which I support [...]

and on the same page says these things:

Incredible things were done in the name of [the political control of economic life], some of them noble and heroic (like resistance to Fascism, and the creation of democratic welfare states), others scarcely matched for wickedness (like Stalin's purges and deliberate famines) and stupidity (like Mao's Great Leap Forward and apparently unintentional but highly foreseeable famines).

and

The history of socialist movements is [...] bound up with the histories of organized labour, of economics and left-wing politics and general, and, less honourably, with that of revolutions and totalitarianism. [...] it had become clear [...] that they [sc. the Soviets] were far, far worse than capitalist democracies [...]

I have to say that none of this sounds very Marxist to me. Shalizi apparently finds revolutions dishonourable; the most notable attempts at (nominally) Marxist states, the USSR and the PRC, he criticizes in very strong terms; he wants most prices to be set by markets (at least this is how I interpret what he says on that page and others it links to).

Oh, here's another bit of evidence:

Sometime between [1956] and 1968 [...] he [sc. Kolakowski] stopped considering himself a Marxist, even a revisionist one [...] though still a socialist and (I think) an atheist.

followed in the next paragraph by

I think his views of socialism and Marxism are absolutely on-target

which seems to me to imply, in particular, that Shalizi doesn't consider himself "a Marxist, even a revisionist one".

He's certainly a leftist, certainly considers himself a socialist, but he seems quite some way from Marxism. (And further still from, e.g., any position taken by the USSR or the PRC.)

This makes his writings on intelligence very frustrating

Does having political views that approximate Marxism imply irrationally-derived views on intelligence? I don't see why it should, but this may simply be a matter of ignorance or oversight on my part.

I am not an expert on Marx but would be unsurprised to hear that he made a bunch of claims that are ill-supported by evidence and have strong implications about intelligence -- say, that The Proletariat is in no way inferior in capabilities, even statistically, to The Bourgeoisie. But to me "somewhere around Marxism in politics" doesn't mean any kind of commitment to believing everything Marx wrote. It isn't obvious to me why someone couldn't hold pretty much any halfway-reasonable opinions about intelligence, while still thinking that it is morally preferable for workers to own the businesses they work for and the equipment they use, that we would collectively be better off with much much more redistribution of wealth than we currently have (or even with the outright abolition of individual property), etc.

In another comment I've given my reasons for doubting that Shalizi is even "somewhere around Marxism in politics". But even if I'm wrong about that, I'm not aware of prior commitments he has that would make him unable to think rationally about intelligence.

Of course it needn't be a matter of prior commitments as such. It could, e.g., be that he is immersed in generally-very-leftist thought (this being either a cause or a consequence of his own leftishness), and that since for whatever reason there's substantial correlation between being a leftist and having one set of views about intelligence rather than another, Shalizi has just absorbed a typically-leftist position on intelligence by osmosis. But, again, the fact that he could have doesn't mean he actually has.

I think the guts of what you're claiming is: Shalizi's views on intelligence are a consequence of his political views; either his political views are not arrived at rationally, or the way his political views have given rise to his views on intelligence are not rational, or both. -- That could well be true, but so far what you've given evidence for is simply that he holds one particular set of political views. How do you get from there to the stronger claim about the relationship between his views on the two topics?