Paul Bloom thinks about moral development:
[M]any psychologists think that the reasoned arguments we make about why we have certain beliefs are mostly post-hoc justifications for gut reactions. As the social psychologist Jonathan Haidt puts it, although we like to think of ourselves as judges, reasoning through cases according to deeply held principles, in reality we are more like lawyers, making arguments for positions that have already been established. This implies we have little conscious control over our sense of right and wrong.
I predict that this theory of morality will be proved wrong in its wholesale rejection of reason.
Emotional responses alone cannot explain one of the most interesting aspects of human nature: that morals evolve. The extent of the average person's sympathies has grown substantially and continues to do so. Contemporary readers of Nature, for example, have different beliefs about the rights of women, racial minorities and homosexuals compared with readers in the late 1800s, and different intuitions about the morality of practices such as slavery, child labour and the abuse of animals for public entertainment. Rational deliberation and debate have played a large part in this development.