"...social evil cannot be resolved by violence. Whatever our theory of evil we know that in practice it lies in the heart of man. It is not something external to him which can be struck and smashed or carted away, or which can be destroyed by an atom bomb. The waging of war only aggravates and spreads the trouble, and the Christian must turn from this to the far more difficult and unpopular task of attacking evil at its root. The only way to end war is to cease to fight, for the devil cannot be driven out by Beelzebub."
-- from "Peace is the Will of God," by Historic Peace Churches and International Fellowship of Reconciliation Committee, Geneva, Switzerland, October 1953.
In Les Miserables, Victor Hugo, I believe, identifies the dual strains of Christianity. There is Javert, who believes in the essentialism of criminality. Once a person reveals himself/herself to be a criminal, then he/she is always a criminal, and so the focus is on sin, judgment, and punishment. And then there is Valjean, who shows a story of change, redemption, and human dignity. Javert's worldview is Manichean: there are the pure good and the pure evil, and it is the duty of the pure good to find and punish the pure evil. Valjean's story reflects more orthodox Christian belief: all humans beings are imbued with inherent dignity, are capable of spiritual redemption, and are worthy of forgiveness.
So when in "Obama's Christian Realism," David Brooks muses on the nature of evil in all humanity, I reach different conclusions than he does. I don't reach the conclusion that evil is out there in the world, making war "necessary." I reflect instead on the potential goodness of an enemy, and that war with the evil in a nation inevitably becomes a war against the goodness in that nation, too (civilian casualties, for example). I reflect on our own side's capacity for evil (something Brooks acknowledges without reaching the same conclusions), which makes me question our side's motives for war, our side's ability to wage it "justly," and our side's abilities to achieve the supposedly noble ends that undergird support for the war.
In the same column, Brooks simplifies, distorts, and straw-mans the views of liberal war opponents:
"But after Vietnam, most liberals moved on. It became unfashionable to talk about evil. Some liberals came to believe in the inherent goodness of man and the limitless possibilities of negotiation."
Far from trumpeting the "inherent goodness of man," many anti-war liberals cite our own side's capacity for evil, and reflect on the ethical and practical problem of using evil means to achieve what might otherwise be a noble end. And I know very few liberals who believe the possibilities of negotiation are "limitless;" rather, war opponents often believe the constructive possibilities and potential effectiveness of negotiation to be far preferable to the costly, destructive, deadly possibilities of war. This is a typical gloss/smear: the war proponent labels the war opponent as the naive idealist. I cite again John Howard Yoder, who in Nevertheless criticizes the "irrational leap of faith" required for the rhetoric that "by supporting a puppet government, we are enabling democracy to grow." Yoder goes on:
"There is no more utopian institution than an idealistic war. [...] War is utopian both in the promises it makes for the future and in the black-and-white way of thinking about the enemy, which it assumes."
Inherent to the argument of evil as a justification for American wars is this: America is good and the evil is out there, so America is justified in fighting the wars America chooses to fight. Evil exists, but America can never be evil, and so America may wage wars against that which America deems evil.
The very fact that "evil" exists is not itself justification for invading a country, for occupying a country, or for bombing a country. Given the death, destruction, and waste of war, including horrors inflicted on the innocent, I would say that war itself is evil.