And therein lies the problem- author isn't just laying out a justification for the invasion, he's laying out a justification for the way Israel is choosing to conduct the invasion as well. The first point is at least arguable from a philosophical, political and historical standpoint (for instance, your point w/ blackfox026 re. the continued existence of Israel). The second...?

Yes, although he tries:

But there is also a second, larger question: How should wars be fought? And here, Israel runs into a problem. Because in the conduct of war, we insist not only that combatants be the sole targets of military action or that steps be taken to reduce civilian deaths. But we also insist on proportionality; that the military value of a target must outweigh the anticipated harm to civilians.

And on this key issue, Israel may seem to fail the test. True, Israel only targets combatants and takes unprecedented efforts at avoiding civilians (making personalized phone calls to civilians before striking areas near them), but can we confidently say that the anticipated harm to innocents is justified by Israel’s expected military gains? The degrading of Hamas’ rocket capabilities, and most of all the destruction of its terrifying network of offensive tunnels (fortified by the limited cement that Israel permitted into Gaza for humanitarian purposes) are valuable military goals. But as the Palestinian death count rises above 500—many of these civilian—I find myself bewildered: Are these tunnels really worth the lives of all those children?

It would seem to come down to this. There are other ways for Israel to go about this invasion (if you take for the sake of argument that they need to invade in the first place) but evidently someone in their Defense Ministry has decided that those options lead to a less acceptable kill to death ratio. I wouldn't be surprised if it's that plain and crass. They can commit more ground troops to more dangerous situations and probably harm many less civilians by decreasing the bombing (although as kb notes it's fucking hard to tell who is who regardless), but they'll lose a few more soldiers. And since neither side particularly thinks the other is human, no Israeli general is going to choose 100 of his own dead and half as many civilian Palestinians instead of the numbers we have now.

Thanks for commenting, I hope I understood the gist of your critique.