A "hidden" God of wrath and vengeance?

Fr. Tim Chesterton recently pointed to an essay by Roger E. Olson:
Every known theistic approach to Old Testament "Texts of Terror"

If one is to take Scripture seriously, one must ponder such texts as I Samuel 13, which recounts the genocidal destruction of Amalek at the express command of the LORD, on the basis of an incident hundreds of years before, when Israel was coming out of Egypt (v.2-3).

How does one reconcile this with the teachings of one who tells us to love our enemies?

I cannot speak to this matter as well as the Rev'd Olson has done, so primarily I point to his discussion, and his comment that all of the nine approaches he outlines "have serious problems."

For the record, I fall into the camp of number 9, Paradoxical Interpretation:

No attempt at harmonization should be exercised; we ought simply to accept at face value the texts of terror and Jesus' teachings about God's love and will (e.g., for peace) and not attempt to diminish either of them or reconcile them. (This is a version of "3" above [Literal interpretation] but attempts to explain it hermeneutically and theologically.)

*Problem: For inquiring minds [this] leads inevitably to belief in a "hidden God" (Luther) behind Jesus who willed (and possibly still wills) extreme violence such as genocidal holy war.

I find Olson's number 8, Narrative Intrerpretation, of interest as well:

God included these texts of terror in the canon as a warning to his people about how far it is possible to misunderstand God's will. To what extent they describe actual, historical events is undecideable at this temporal remove and is unimportant.

I do not subscribe to the second sentence of this, because it is all too plausible that the mass slaughters described in these passages actually took place. They are characteristic of our behavior toward one another throughout history.

But are these accounts indeed in the canon as a warning? If so, they are a dire warning indeed. For if the prophet Samuel (and Moses, for that matter: see Numbers 21) can so completely misunderstand the will of God, what of lesser folk such as us? To mention an example from recent history, it is easy to construct a Biblical justification from both Old and New Testaments for the practice of slavery, and as recently as 150 years ago, many Americans would have subscribed to such a doctrine. It seemed that the ethical issues for a Christian lay in the manner in which one should act toward one's slaves and in how slaves should act toward their masters, not in whether or not there should be slavery in the first place.

At this distance, it is clear that slavery is wrong, and has always been wrong. But where else are we equally wrong in our understanding of the will of God, so wrong that we cannot see it?