People tend to have a very big stake in their own goodness. So it figures that they’d really want moral truths to be simple and clear cut, and the less they’ve thought critically about hard moral issues, the simpler and more clear cut the better. But if we step outside our tendency towards self righteousness for a minute, there is really no reason to expect ethics to be somehow more simple and straightforward than, say, physics or chemistry. Most of us don’t have a hard time admitting to ourselves that we don’t know all that much about physics or chemistry. But to admit that we don’t know so much about what’s good or right is much harder. That would cast some doubt on our own goodness and many people find this intolerable.
This tendency towards self-righteousness also explains much of the appeal of moral relativism. Moral relativism rejects moral absolutes and fans of moral relativism see this as promoting more open minded and tolerance of those with other views. There are good reasons to doubt that moral relativism delivers the goods on the virtues of open mindedness and tolerance. Moral relativism is the view that what is right relative to a group (culture or individual) is whatever is deemed right relative to that group (culture or individual). But there is nothing in this view that speaks against a group (culture or individual) deeming narrow-minded intolerance a good thing. Moral Relativism deems bigotry good relative to the bigot.
But let’s focus on the role of self-righteousness here. Moral relativism deems everyone (or every group) right relative to themselves. On this view I can maintain that I am right (no matter how narrow-minded and uncritical my view is) so long as I’m only asserting that right just means right relative to me (or my group). So moral relativism invites everyone to be perfectly self-righteous relative to themselves. And it thereby prevents reasoning about ethics from playing any useful role in adjudicating conflicts. What tools does this leave us for dealing with conflicts? Well, there is always power politics, or if that doesn’t work, brute force.
An alternative to both moral absolutism and moral relativism would be to take inquiry into morality seriously. That is, to take morality to be the sort of thing we can learn about through critically examining evidence and argument. But here’s the catch: taking inquiry into morality seriously requires acknowledging that maybe we don’t already know what is good and right. That is, it requires abandoning our self-righteousness.