But we should recognize this new model is not some aberration, not a form of psychopathology. It is cross-culturally a very common way for humans to approach morality, a.k.a. "tribalism." Those who belong to my clan, I'm obliged to treat well. Those who are outside my clan are outside my moral concern. It is such moral tribalism that leads these school killers to warn friends to stay away (killing a friend would be wrong).
Morality is personal. What's right for you isn't necessarily right for me. And who you wrong doesn't matter to me, as long it's not me: "I'm not going to dislike him just because he killed people."
The old moral model that dominated Western civilization was based on the opposite premise: Moral rules are the same for everybody, everywhere. Kant called it the universal imperative. More recently it's been dubbed "objective morality." Belief in an absolute moral code transcending personal tastes and affections is not an inevitability. It is the product of two millennia of thinking and teaching about God, reason and human nature. And it can disappear, it seems, virtually overnight.
Maggie Gallagher is a nationally syndicated columnist, a leading voice in the new marriage movement and co-author of The Case for Marriage: Why Married People Are Happier, Healthier, and Better Off Financially.