I think a person's politics is a good indicator of how rational they are. Current research bears me out that authoritarians are more susceptible to motivated reasoning (the current term of art for confirmation bias). Chris Mooney makes an excellent case that epistemic closure is more prominent among conservatives than it is among liberals. Climate change denial, free market fundamentalism, and a broad assortment of conspiracy theories and paranoid delusions are rampant on the far right today. The left is relatively free of such hysteria.
So, I agree with this at a very weak level. The question is how good an indicator is this? For example, I know a very successful mathematician who has extreme right-wing politics, and another who has extreme left-wing politics. I know a linguist who is a monarchist. The fact is that humans can be highly rational in one area while extremely irrational in another. Look for example at how much of the left has extreme anti-nuclear power, anti-GMO and pro-alt med views that have little connection to evidence. The degree to which the left is "relatively free" has the word "relative" doing a lot of work in that sentence. Moreover, Moldbug's views don't fit into a standard notion of far-right.
Another issue to point out is that the studies which show a difference between left-wing and right-wing cognition are to a large extent limited: The differences in populations are quite small. Moreover, by other metrics, conservatives have more science knowledge than liberals on average. In fact, the GSS data strongly suggests that in general the most stupid, ignorant people are actually the political moderates. They have lower average vocab, and on average perform more poorly at answering basic science questions.
I don't think a royalist follower of von Mises has anything interesting to say. Those who would admire such even less so.
So I'm deeply confused by this statement. You seem to be asserting that "Person X who says A will be extremely unlikely to have anything useful to say." And asserting that "If Person Y thinks that Person X has interesting things to say about B despite X's declaration of A, that makes the person Y even less likely to have useful things to say?" I'm curious, if we had a Person Z who pointed out that Y had interesting thing to say about issue C, would Z become even further less useful to listen to?
I've seen several people on Less Wrong recommend Mencius Moldbug's writings, and I've been curious about how he became so popular here. He's certainly an interesting thinker, but he's rather obscure and doesn't have any obvious connection to Less Wrong, so I'm wondering where this overlap in readership came from.
[EDIT by E.Y.: The answer is that he's not popular here. The 2012 LW annual survey showed 2.5% (30 of 1195 responses) identified as 'reactionary' or 'Moldbuggian'. To the extent this is greater than population average, it seems sufficiently explained by Moldbug having commented on the early Overcoming Bias econblog before LW forked from it, bringing with some of his own pre-existing audience. I cannot remember running across anyone talking about Moldbug on LW, at all, besides this post, in the last year or so. Since this page has now risen to the first page of Google results for Mencius Moldbug due to LW's high pagerank, and on at least one occasion sloppy / agenda-promoting journalists such as Klint Finley have found it convenient to pretend to an alternate reality (where Moldbug is popular on LW and Hacker News due to speaking out for angry entitled Silicon Valley elites, or something), a correction in the post seems deserved. See also the Anti-Reactionary FAQ by Scott Alexander (aka Yvain, LW's second-highest-karma user). --EY]