I recommend this book.
In The Righteous Mind, Jonathan Haidt shows that different people have different foundations which underlie their moral judgments or beliefs.
On the "left," the foundations of fairness and charity are more prominent. On the "right," the foundations of loyalty and "purity" are more prominent.
These styles or foundations may be propagated in culture or family upbringing, but also are partly influenced by heredity (genes). In the middle part of the book, Haidt argues that each of these moral foundations can convey improved survival or natural selective advantage to whole groups. For example, a group which values loyalty very strongly as a moral foundation is more like to be cohesive, and therefore more resilient to various stresses, including warfare or internal discord.
Haidt concludes his book with a strong message that we should empathize with people or groups which have different moral foundations, rather than simply fight with them or view them as enemies. He espouses the goal of befriending opponents, including those who have different political or religious beliefs or moral foundations. Such friendship would then reduce extremes of polarization and conflict, and allow groups to move forward more peacefully.
I respect his thesis very much, of cultivating understanding and empathy for people or groups which have different moral, religious, or political beliefs than one's own. In a psychotherapy environment, such empathy is required in order for progress to occur, even when the therapist may object strongly to aspects of the patient's behaviour.
But I have some criticisms of Haidt's thesis:
Haidt seems to disparage the importance of reason or rationality. In a type of "straw man" argument, he suggests that "reason" without other moral foundations such as loyalty, is insufficient or even pathological. He uses a metaphor of a person or a mind being like an elephant, a powerful creature guided by instincts and passions, with the "rider" of the elephant being our "reason" or logical faculties. The "rider" is described as a recent evolutionary development, intended to serve the elephant, rather than rule over it.
He anticipates in the book that some people will disagree with him on this. I certainly do. I do not disagree that the development of sophisticated reason or rationality is a recent development in evolutionary history, that it indeed did develop in service to the "elephant," and that there are strong selective advantages for "non-rational" qualities, which remain prevalent in nature. But the evolutionary presence of traits is not evidence of their high moral value.
Modern rationality is the foundation of the justice system. Imagine a court system, a scientific lab, a factory producing safety equipment, or a spacecraft agency such as NASA, which would not hold reason as the highest foundation in its decision-making, but instead would consider "loyalty" or "purity" as most important. Such foundations would, and often have, led to disaster.
I realize that some applications of reason may in retrospect prove not so "reasonable" after all. Reason is always fallible, and can be the foundation of huge mistakes--not just technical failures due to mistaken ideas that were apparently well-supported at the time (e.g. the belief in medical remedies such as bloodletting), but also moral catastrophes. But the process of reason requires it to be flexible, to monitor itself for mistakes, to be willing to make corrections when new information arises. This differs from "loyalty" which is by definition resistant to change despite the arrival of new information.
"Loyalty" could be considered a component of "reason" which requires a waiting period before acting on new ideas. It could be like electing a senator for a 6 year term, with other representatives elected for 2 year terms. The senators would be more resistant to rapid or erratic whims of a capricious populace, while the representatives would be poised to act more quickly; the two chambers would ideally lead to an effective equilibrium, sensitive to change, but not impulsively so.
I am not saying that "loyalty" or "purity" are unimportant, but they cannot be viewed as morally equivalent to reason, on some kind of equal footing, such that differences between people can be understood simply as cultural variation.
I was bothered in Haidt's book by his passing disparaging reference to "new atheists" such as Richard Dawkins, more or less dismissing the value of their ideas without acknowledging their wisdom or contribution. There are major problems with these thinkers which warrant fair criticism, but they do deserve respect and attention. This is ironically contrary to Haidt's best conclusion, which is to have some empathy and respect for viewpoints different from one's own.
I am more allied to scholars such as Steven Pinker or Paul Bloom, who are "rationalists" in their approach to psychology and morality. But I have to admit that Jonathan Haidt is an important thinker as well, and deserves respect and attention.
Any author of a book has a tendency to have some inflexibility in their position afterwards, due to several psychological biases. If you have publicly asserted a position, and have become famous for it, you are more likely to maintain it in order to appear consistent, even if there are good arguments against it. There can be some degree of ego involved as well--people don't like to admit that they are wrong. I wish there was a little bit more humility when scholars or experts assert positions on these issues.
I am not an author (except for this modest blog), but I know that I have an ego as well, and I would have a tendency to defend positions that I have asserted, even when they may need to be changed or adapted. I need to watch this tendency in myself, as we all do in ourselves.
In some cases, it may not be possible to have a friendly, empathic dialogue in a setting of conflict, oppression, or injustice. Haidt does not explore this type of scenario adequately. Friendship and empathy are neglected in the management of conflict and polarization, but it is important to acknowledge as well that some of the necessary forces of positive change and justice can be rather more difficult and conflict-ridden.