An 800 pound gorilla in the room of justice, particularly for some Christians, is a horror of taking any action that may be construed as violent. To violate someone's personal space, whether physically, psychologically or spiritually and cause injury is simply not done among practicing Christians. Only non-violent strategies are permissable, and the rule of thumb is to "follow Jesus," if need be, to the cross.
And yet, and yet.... Edmond Burke's purported sentiment of 1795, "The only thing necessary for the triumph of evil is for good men do nothing," raises a slew of questions regarding the use of force for the sake of saving lives rather than increasing the vulnerability of those put at risk if "good" men stand back and do nothing.
Bonhoeffer decided for violence. My only problem with Bonhoeffer's choice is lies in his retention of the title, "pastor." Somehow, placing a bomb in order to kill Hitler if not his cronies doesn't square with that particular calling, at least for me.
The Church (one, holy Apostolic Church of varigated sorts, types, theologies, histories) has taken both pro and con positions on the use of force over the centuries with no fixed pole of absolutism governing the decisions: "Yes" on the one hand, "No" on the other.
Under certain conditions, force may be necessary, depending upon the goal to be achieved. A specious and self-serving answer to be sure, but what do we mean by "objective" or "self-interest" here? Definitions depend not merely upon the situation to be faced but upon interpretations describing that particular situation leading to particular actions. What I would look for is an interpretation that regards the other as one step up the ladder of value beyond my capacity to interpret a situation in which violence dominates. In other words, the actual "other" must be more interesting than my interpretation of who that "other" is. Or, the unknown and unknowable creature is more important than my mere interpretation of that very creature in her or his context (sitz im Leben). Such a statement smacks of pacificism, until I look at the victims who a decision "to do nothing" will produce by actually dis-valuing those put into harm's way from my decision to do "nothing."
Neither Augustine's "just war theory," or Aquinas' argument for self-defense (suicide is a mortal sin), for example, does "justice" to contemporary conflicts in which violence is employed to generate peace through terror: a modern attempt to gain a Pax Romana rather than a Pax Christi. If I look carefully at ISIS I see no difference between Algerian assassins of a 15 years ago who snuck into villages at night and massacred whole families and the behavior of ISIS or Boko Haram. The latter took place at night, while the former goes on at any hour. I cannot say that neither has anything to do with me, because it does. It does, because I am aware of these atrocities, and that awareness shapes a certain responsibility towards the ones slaughtered today and those who will be slaughtered tomorrow. Religion doesn't matter here. Blaming or exonerating Islam is not the point. We can blame or exonerate Christianity on similar grounds. What counts is the living and dying of just one creature of God. Just one. In deconstructionist ethics, this concern has been called "the recovery of particularity."
And it is that "just one," that forms my decision to engage in military action against ISIL or ISIS or such behavior by whatever name through the actions of my goverment. The horror for me is unendurable. It is difficult to understand the proposed isolationism of Rev. Parsons. Reminicient of the 1930's, such isolationism aided and abetted the agenda of two totalitarian regimes: Fascism and Communism in the pact between Hitler and Stalin. As Stalin engaged in his purges and Hitler determined to purge the human race of anybody he didn't like, isolationists, happily self-defined as pacifists, helped pave the way towards World War II and the slaughter of innocents on a scale much more vast than ISIS, so far, has managed. So far.
Non-violent strategies can work only when one's opponents use violence as a last resort. But from what I have come to understand, violence is the only strategy for achieving anything at all for groups such as ISIS. I support military intervention in this instance.