Why do secularists make "just war" arguments?

For example, take Massimo Pigliucci's argument for bombing Libya. It's a "just war" argument.

I raise this for several reasons.

First, most notably, the idea of "just war" arose from Christian dogmatic theology, namely starting with St. Augustine. From Thomas Aquinas, and onward, it got wrung through a sophistic wringer, and not just by Catholics, once the Protestant Reformation arrived.

Now, could one argue for something similar to a "just war" from a secularist point of view and with secularist bolstering?

One could try, I'll certainly concede, using tools such as evolutionary psychology. And please, only the real thing, not Pop Ev Psych.

But, a philosopher like Pigliucci ought to know that the idea of "justice" is philosophically iffy on utilitarian and other grounds.

First, can we even talk about "justice" in the abstract, whether retributive or distributive?

With Walter Kaufmann, I say no. I specifically refer to his hugely thought-provoking book "Without Guilt and Justice," which pretty thoroughly eviscerates John Rawls like an eight-inch herring.

To put it simply, neither form of justice, in the abstract, can be universally applied in the concrete. To execute what seems "just" to some, even many, will always or nearly so be unjust to somebody.

So, should we let a utilitarian hedonistic calculus apply?

But, that leads me to the old Chinese or pseudo-Chinese parable, with the ongoing refrain of "could be good, could be bad."

What seems "just" to and/or for the majority now may not five months, five years or five decades from now. Maybe not even five days from now.

So, no, we shouldn't.

So, what CAN philosophy tell us in situations like this.

First of all, looking elsewhere in the East, something like Taoism can tell us all decisions are fraught with uncertainties and shades of gray.

Second, we can move on to Iranian philosopher Idries Shah, who uttered the aphorism, "There are never just two sides to an issue." While that itself is a bit too black-and-white for me, it nonetheless has a large kernel of truth.

Take the air strikes against Libya.

There is:
1. The tribal rebels' side (or sides, depending on how much or how little coherence they have;
2. The U.S. side;
3. The Franco-British side;
4. The Turkish side;
5. The Arab League side;
6. Gadhafi's side;
7. The Russian side;
8. And, though we've not heard from Beijing yet, surely, the Chinese side.

Even if we narrow the issue of "justice" here, rather than play realpolitik, at least the first three, if not the first five, are all legitimate "sides." And, all with different definitions, at least in narrow particulars if not major strands, as to what might be "just."

And, also, since "just war" ultimately has religious roots, shouldn't we be careful about it for that reason, too? Monotheistic religions deal in black and white; I prefer my philosophy with more nuance. And, my secularism in general.