Jonathan Haidt kindly let me read an earlier version of The Righteous Mind last June.  Here are the comments I sent him.  I haven’t seen the final version, so perhaps he revised the book in response.

Jonathan, I finally finished the first eight chapters.  What an incredible
work of scholarship.  Amazing.

My two big comments:

1. Empirically, there’s just one big problem: You’re too quick to accept
liberal and conservative rhetoric about their “massive disagreements”
when your own data show that these differences are only marginal.  At
least in data I’m familiar with, only about 6% of Americans *total*
describe themselves as “very liberal” or “very
conservative.”  And even their belief gaps average around 1 point on
a 1-5 scale.  If you focus on the merely liberal and the merely
conservative, the differences are quite small.

From an abstract philosophical point of view, American liberals and
conservatives are all nationalists first, and social democrats second. The only
thing “extreme” about the liberal-conservative divide is the animus
they bear each other despite their fundamental agreement, as I argue in this

American liberals and conservatives are no more fundamentally opposed than
Catholics and Protestants.  There are marginal disagreements in both
cases.  And both sides blow them all out of proportion to condemn the
other side as the Antichrist.

2. I studied philosophy for years before I became interested in
psychology.  And frankly, it’s hard to imagine any moral objectivist
taking Kohlberg’s project seriously.  Moral agreement is a red herring.
 There’s massive disagreement around the world on the origins of the
universe and life, too.  But there’s no need to deny the reality of
disagreement to maintain that one theory about the origins of the universe and
life is true and the rest are wrong.

If you want more details on moral objectivism as philosophers conceive it,
check out this excellent early essay by U Colorado phil prof Michael Huemer. 
This essay later became his book, Ethical

All the evidence you present on the fallibility of moral judgment is
important.  But it’s one thing to say, “People’s moral judgment is
biased in many ways,” and another to deny that moral truth exists. 
It’s easy to scoff at the idea of “moral truth,” but consider: Does
anyone imagine that the evidence on self-enhancement bias undermines the view
that some people are better at various tasks than others?

In any case, great work.