There's truth in this piece by Jonathan Chait, but that truth can't sustain the argument he tries to make.

I agree that it's "silly" (in his words) to judge the morality of a war based on the casualties inflicted by each side.  I think Israel's attack on Hezbollah is justified, given Hezbollah's periodic and sustained rocket attacks on Israeli civilians, its cross-border raid to kill and capture Israeli soldiers and its alliance with a country working to acquire nuclear weapons and currently led by a man who ruminates publicly on the impending destruction of Israel.  And it's true that Hezbollah relies on its ability to disappear into the civilian population, and is therefore responsible for civilian casualties the Israelis inflict while seeking out military targets in southern Lebanon.  But I think Chait moves into dangerous territory when he writes:

If those strikes are carrying out their intended effect, then it's a justifiable response. If they're not, then it's not justifiable.

But proportionality has nothing to do with it. If Israel was attacking Lebanon's infrastructure at random, then it would be wrong even if it killed fewer Lebanese than Hezbollah killed Israelis.

I think this is the logic that causes reasonable and humane people to start signing off on everything a government does in the name of a noble end.  I'm not in Lebanon, I'm not in Israel, I'm in no position to judge whether every Israeli airstrike is a necessary part of its operation against Hezbollah.  Neither is Chait.  He writes:

Israel says it has massively degraded Hezbollah's store of rockets. We shouldn't take Israel's word on that, for obvious reasons. (Any country overstates the effectiveness of its military operations from time to time.)

That's an admirable level of skepticism when it comes to what any government—not just Israel—claims about its own military operations.  But Chait also says:

Israel says every one of its air strikes has a specific strategic and military rationale. The attacks on Lebanon's civilian infrastructure are not "collective punishment," they're an attempt to prevent Hezbollah from transporting the captured soldiers to Iran and to prevent Iran and Syria from resupplying Hezbollah. Where Israel has bombed civilian areas, it has been in an attempt to strike Hezbollah's rockets.

I'm not sure what evidence he has of that, other than the same assurances from Israel that he discounts when it comes to the purely operational aspects of the Israeli campaign.  Frankly, it wouldn't surprise me at all if part of Israel's bombing campaign was "collective punishment" designed to impress upon the Lebanese government and the people of Lebanon that it is very dangerous to turn a blind eye to Hezbollah's attacks on Israel.  Would that be justified, given the nature of the threat Hezbollah poses?  It's a more difficult issue than simply assuming out of hand that every Israeli airstrike has a purely tactical purpose.  It gets to the question Chait never addresses, which is exactly what the limit is when it comes to defending a country and its citizens.

He's absolutely right about the lower limit, but what's the upper limit?  It's not helpful to jump, as Chait does, to history's most terrible and destructive moments:

During World War II, Germany sunk a lot of American ships and declared war on us, and in return we flattened its cities, killed or captured hundreds of thousands of its solders and occupied its land. That was hardly a proportionate response.

Let's be clear about Nazi Germany—its attacks on the United States may have been minimal but by the time we began massive bombing raids against German cities it was clear that the Nazis had both the capability and the intention to slaughter millions of people and to subject Europe to unending tyranny and genocide.  Before a single American bomb fell on Germany the Nazis had already invaded Poland, killed tens if not hundreds of thousands of non-Jewish Poles, ghettoized and begun the systematic slaugher of millions of Polish Jews, opened Dachau and Auschwitz, invaded Norway, invaded Denmark, invaded Holland (leveling Rotterdam for demonstration purposes in the process), invaded Belgium, invaded France, carpet bombed London, invaded Yugoslavia, invaded Greece and Crete, invaded Russia, murdered hundreds of thousands if not millions of Soviet Jews, murdered hundreds of thousands if not millions of Soviet prisoners of war, issued the "Night and Fog" decree authorizing the secret deportation and exection of suspected resistance fighters in western Europe, declared war on the United States days after Pearl Harbor, and come very close to destroying the British empire in 1940 and the Soviet Union in 1941.

I don't mean to minimize Hezbollah's criminality when I say a comparison to the Nazis is out of proportion.

Chait's point isn’t to put Hezbollah in the same league as the Nazis (at least not in terms of its capabilities; its intentions are monstrous).  But it's telling that he immediately reaches for that analogy.  You can pretty much justify anything when you're doing it to Nazi Germany.  I doubt Chait’s reference to Allied bombing of German cities outraged many people, even though that bombing killed about 100,000 German children during the Second World War.  Chait concludes:

We won't know for some time whether Israel has really taken a chunk out of Hezbollah. Either way, balancing the number of dead Israelis against dead Lebanese tells us nothing.

I don't think Chait is really arguing this—he's really arguing that he knows Israel will keep civilian casualties within a level that he defines to be acceptable.  He should make that argument, instead of constructing a more complicated one that justifies any attack at all as long as it “works.”