First Haidt proposes a model for the relationship of morality / reason modifying Humes; reason is the slave of passion. The modification would be stipulating this is a roman master and an educated greek slave who is a trusted advisor, and whose fortunes are tied to the gens. That is virtually all reason could also be described as rationalization and is post hoc.
I have no problem with this. In high school, I was challenged by my religion teachers, as Mormons are, to find out for myself about the truthfulness of God, Christ, and the LDS Churches claims to authority/revelation. So I spent a lot of time marshaling arguments for and against. I found that I could establish a pretty strong case either way, depending on what I wanted to do. I concluded that reason itself would be useless in making this determination. So I put all my efforts in praying, reaching out to God. Words were given to me, “You already know its true.” and those specific memories came to mind. So his statement that we evolved to be lawyers and not scientists is more or less in line with my pre-existing thoughts. It also jives well with the conclusions that seem to follow from Turchins work on large scale cooperation – basically the genius of humankind is social, all other intelligence evolved either to support that or is a legacy of primates. When I was studying intelligence I recall a test of chimpanzees for working memory (thought to be one of the building blocks of high IQ v. low IQ in people). The test is n-back, a good score for humans is 5-8, for a chimp 30-50 is reasonable. Perhaps a good society has already allowed us to offload a lot of cognitive function, to the cloud of other people? And we use the surplus to maintain bigger more integrated societies?
Moving on, I think that the political focus was a mistake as it took away from the main points. On the other hand without tying it to politics, it is likely I would never have heard of the book. Implications of it is that to form strong sacrificing groups and outgroup is needed. One world government has some problems built in. That’s not to say a nation state status quo is without issues. It appears the democratic norms (real rights, privileges and responsibility to little people) came about as a side effect of mass wars. Well, it seems mass war is dead, and if it weren’t we’d probably want to kill it. Well like the greeks we might be done with mass war, but as with the romans it may not be done with us.