"Rigged" was a bad choice of word on my part, since it suggests intentional manipulation, and as I've already written, I'm not suggesting anything like that in Haidt's case. Rather, it's a matter of deeply internalized biases. More specifically, the problem is that with enough motivation, almost anything can be rationalized in terms of harm and fairness, and people whose favored ideology emphasizes these elements are likely to invent such rationalizations for their own specific norms of purity, sacredness, group loyalty, and authority. Haidt's approach ends up heavily biased because it correctly recognizes these latter elements in those cases where they are more or less explicit (which happen to be mostly on the political right), while at the same time failing to uncover them when they exist under a veneer of rationalizations in terms of harm and fairness.

Now, the concrete examples of leftist purity manifested in nutritionist and environmentalist ways are recognized by Haidt, as another commenter has already noted. (Though, in my opinion, he is certainly biased in underplaying their overall importance.) However, I believe there are other examples that illustrate the problem even better.

Take for example the norms about sexual matters. One puzzle I've always found fascinating is why, for modern liberals, support for laissez-faire in matters of sex is so strikingly correlated with opposition to laissez-faire in economic matters and support for paternalistic government regulation in pretty much everything else. After all, most of the standard arguments of liberals against economic laissez-faire and in favor of government paternalism hold just as well for sexual matters. (Arguably, they are even stronger in the latter case -- just consider how much it involves in terms of zero- and negative-sum games, tremendous inequalities, common patterns of irrational behavior, health concerns, discrimination across protected categories, etc., etc.) Yet an attempt to apply these arguments to sex immediately triggers a strong negative reaction that can't be justified by any reasonable argument based on harm or fairness.

From this, it seems pretty clear that modern liberalism incorporates a strong element of sacredness associated with individual autonomy in matters of sex. This, of course, is nothing very surprising, considering that strong norms of sacredness regulating sex are a human universal. Yet even if he had a perfectly unbiased view of the matter, how could Haidt possibly reveal this element in his questionnaires without violating the associated norms of sacredness as they apply to the public discourse about sex-related topics?

Another fascinating topic is the peculiar way in which in-group morality is commonly manifested on the left. What I have in mind is the phenomenon that was discussed recently on LW in a thread about Orwell's essay "Notes on Nationalism," which Orwell termed "transferred nationalism." See this subthread, in which I made some points whose relevance in this context should be clear. Again, this is something highly relevant in the real world, whose discussion however requires much more subtlety and de-biasing than anything within the reach of Haidt's questionnaires.

I'd like to elaborate on some examples of authority norms that are common on the left too, but right now I'm short on time. I'll get back to it if this thread remains active in the next few days.