Jonathan Haidt's Righteous Mind is a delightfully written and thought-provoking book. He covers quite a lot about morality before he moves to the punch line that you may have seen in his TED talk or in various interviews he gives. (Essentially, he explains how the morality of conservatives and liberals differs and why.)
He argues that morality evolved as a means to win approval, not to find the truth. You make think it is "true" that it's bad to deny rights to (fill in the blank with everything from Tutsis to Jews to women to Jewish women Tutsis) but discovering or arguing for something that feels "true" to you, curiously enough, is not the role of morality. Morality does show up as an obviously right or obviously wrong thing to us, but, those judgments that feel so real to us turn out not to be universal truths. So while it may be that what is "true" evolves (Philistines should be killed, debt is sinful, women should not vote, gays should be imprisoned, animals are food, work need not be fulfilling ...) over time, your tribal identity depends on a clear statement of morality that "feels" true at a particular time.
Science and skepticism are for the discovery of truth. And that is uncomfortable, requiring questioning and living in doubt and hard work. Very few people are scientists. Morality is for winning group approval so that you prove you can be trusted. It's much easier than science and nearly everyone is moral (although not necessarily in a way that your group might recognize).
Perhaps that's obvious to everyone else. To me, it felt like a remarkable kind of revelation.