In Judaism, one of the enduring symbols is Amalek, a tribe whose deceitful ambush has come to symbolize an enemy to whom one can't afford to demonstrate mercy. Gershom Gorenberg relates an interesting twist on the Amalek story that changes the call to hate the other to a call for moral responsibility for the other:
Amalek, according to the books of Exodus and Deuteronomy, is the name of the tribe that attacked the Israelites on their way out of Egypt, on the road from slavery to freedom. You can regard this as ancient history. But history is remembered as our story, and in Jewish mythic consciousness, Amalek became a name for hate embodied.
From there, it's an easy jump - for the fearful and the angry, and for those embodying a fair amount of hatred themselves - to label a present-day enemy as Amalek. The formula "Amalek = ____" transforms a real-world conflict into a metaphysical one, and gives theological sanction to fury. Since Haman is described in the Book of Esther as a descendant of Amalek, and Esther is read on Purim, some misuse the carnival holiday to dress Judaism in a dark costume of rage.
And others remove that awful mask. Twenty-five years ago I heard an interpretation of the Amalek myth that transforms it into moral obligation. It was entirely rooted in rabbinic tradition - and served as proof that the meaning of the text is the responsibility of the interpreter. I remain uncertain that the man from which I heard it was really there. Here's the story, as I wrote it up sometime afterward.
Go read the story Gorenberg wrote up.