Broad, scientific approach to understanding the biology of human behavior.
"Thinking Fast and Slow" by Kahneman and "The Believing Brain" by Shermer in terms of understanding neuroscience and the way our brains, opinions and behaviors come about.
We've created a culture where we all operate under the illusion that we need to be right. We convince ourselves that our thoughts and actions stem from some innate ability to realize and appreciate a guiding, transcendent truth, whether it be social, spiritual or logical. The humbling reality is that we have selfish genes which utilize complex modules to ensure their survival. Haidt cogently describes our biology with both scientific and symbolic aplomb.
As a biologist and physician, I have great appreciation for this perspective. I particularly appreciate the analogy between our ethical "taste" modules and our literal gustatory senses. We cannot fight the fact that we are hardwired to respond to these tastes and indulging them initiates the neurochemical cascade which, if deprived, would leave us bereft of the true experience of humanness.
Continuing this analogy, I would attempt to demonstrate where Haidt possibly falls short in helping both himself and his reader best apply their enhanced understanding of human and cultural biology.
As our ethical "tastes" for sanctity, loyalty and authority have a place in maintaining safety and wellness, our taste for sugar and fat has served our species greatly in times of scarcity. The utility of these modules is entirely contextual though. In the United States (my very divided country), we live in relative abundance. The vast majority has an excess of calories as well as social safety. The context has changed and indulging our hunger for fat and sugar as well as symbolic tribal loyalty, sanctity and authoritarian acquiescence has very negative consequences. We benefit when we recognize mal-adaptive application of natural tendencies. There is little risk that we will go hungry if we forgo calories and there is little risk that the fabric of our society (and our own differential survivability) will fall apart if we question authority, symbolism or factionism.
We live in a country of abundance and safety. Indulging these tastes is causing an epidemic of obesity, hypertension, diabetes and heart disease. Could not the same be happening when insisting on applying unnecessary ethical modules? I enjoy being clean AND my understanding of germs and public health tells me I don't need to be continually vigilant. I enjoy my groups of shared interest AND I don't need to denigrate or vilify any groups to which I do not belong. I appreciate order AND I know rules and laws exist to serve a social purpose but my eternal soul is not at risk should I fail to worship compliance.
Haidt is correct in that Conservatives indulge their ethical tastes more broadly. Their message is an ethical meal that satisfies many of our cravings. The Liberterian and Liberal ideologies are less appealing to a broad population... but dining at their table more often may be the only way of preventing the epidemic of ethical indulgence?