I think Michael Walzer is right to say that most of the “proportionality” talk around Hamas rocket fire and Israel’s attack on Gaza has been confused and irrelevant. But strangely this mostly leads him to go on talking about proportionality rather than considering other issues.
I would say, however, that what’s most relevant for both sides here are separate elements of just war theory — possession of “right intention” and “reasonable prospects for success.” First from the Hamas side. As Israel’s critics will happily let you know, Palestinians have just cause for fighting against Israel. But Hamas’ actual cause isn’t the just cause of Palestinian independence but an unjust cause of aggression against Israel. And even if Hamas were fighting for a just cause, their method of untargeted rocket fire has no reasonable prospects for success. If the way the world worked was that you should some rockets at Sderot, damage some buildings and hurt a few people, and then suddenly Israeli officials are ready to shake hands on a deal that ends the occupation forever you might be tempted to say that the loss of civilian life would be proportionate to the ends being pursued. But that’s not how the world works and it doesn’t characterize Hamas’ war aims.
A lot of commentators seem to want to believe that the situation on the Israeli side is very different from this. In fact, I think it’s only a little different. In terms of “right intention” this is where the settlements come into play. As long as Israel is occupying illegal settlements in Palestinian territory, restricting Palestinian movement in order to defend them, and indeed expanding the settlements it becomes difficult to view any Israeli activity as purely defensive in nature. And, again, if the way the world worked was that attacking Gaza and causing suffering there led Palestinians to say “you know, these Hamas guys are bloodthirsty maniacs — let’s put some non-violent moderates in charge” you could understand this campaign as having reasonable prospects of success at securing enduring safety from Hamas rocket fire. But that’s not how the world works. So asking what kinds of Israeli actions might or might not be “proportionate” to those war aims is really neither here nor there. Everyone understands that this round of fighting will stop some day soon, but that the halt in fighting won’t create a permanent end to rocket fire.