Why did the U.S. intervene in the internal conflicts of Libya but not Somalia? A U.S. general said (something like) "We're not consistent, but look out for American interests." Of course, staying true to American interests is a kind of consistency.
This is the dichotomy: acting based on the idea that the same rules apply to everyone, versus acting in the interest of "I" or "the self" only. History is a constant tradeoff between these two.
If I'm not mistaken, this is known in some fields, such as economics (refs?).
Sociobiologist E. O. Wilson's forthcoming book "The Social Conquest of Earth" posits the same thing. Our genes predispose us to act based on group selection and, alternatively, individual selection. "Group selection brings about virtue, and--this is an oversimplification, but--individual selection, which is competing with it, creates sin. That, in a nutshell, is an explanation of the human condition." [The Atlantic, Nov. 2011].
This seems sound.