Despite the bombings of two Palestinian schools that the UN had designated civilian sanctuaries, let us assume that Israeli forces have not been attacking civilians intentionally. It is possible that the killing of Palestinian civilians is a foreseeable but the unintended side effect of defensive military action has been disproportionate in relation to the aim of protecting Israeli civilians and soldiers from attacks by Palestinian fighters.
To preempt misunderstanding, let us accept that Hamas’s indiscriminate rocket attacks on Israel are wrong, as are its storing weapons in schools, private homes, and mosques, its locating entrances to tunnels in the same places, and its firing missiles from civilian areas in a way that attracts Israeli retaliatory fire to those areas. But he believes that Palestinian resistance to Israel’s unjust quarantine of Gaza and unjust occupation and settlement of the West Bank ought, for both moral and prudential reasons, is nonviolent in character.
One might think that it requires no argument to show that the killing of Palestinian civilians has been disproportionate, since no Israeli civilians were killed by Hamas in 2013 or 2014 before Israel began bombing Gaza earlier this summer in response to the killing—not, apparently, under the direct orders of Hamas—of three Israeli teenagers. But proportionality in defence does not depend on a comparison between harms one has suffered in the past and harms one causes in response. That is something different: proportionality in reprisal. Proportionality in defence is instead a relation between harms one causes and harms one seeks to avert in the future. And granting that Israel’s war has been defensive rather than retaliatory or punitive in its aims and that Israel’s main aims have been to prevent further rocket attacks from Gaza and to destroy the tunnels that have enabled Palestinian fighters to enter Israel to kill or abduct Israeli soldiers, the issue of proportionality still remains.
In the effort to achieve these aims, Israeli policy has been to give near-absolute priority to the protection of its own civilians and soldiers over the avoidance of killing Palestinian civilians. The permissibility of giving priority to the protection of one’s own soldiers (“force protection”) was advocated in articles by certain Israeli just-war theorists in the middle of the last decade and these seem to have influenced the conduct of the invasion of Gaza in 2008-2009, which in turn set the precedent for the way the current invasion is being conducted. Thus the New York Times reported on 1st August that, as Israeli forces have advanced, “they have pummeled neighborhoods with heavy artillery, which analysts said was militarily necessary to safeguard soldiers. … ‘In a dense urban environment, you need to use aggressive force to save soldiers’ lives,’ [Amos] Harel, the military affairs analyst, said.”
There are thus two questions:
(1) Are the killings of Palestinian civilians proportionate in relation to the aim of protecting Israeli civilians?
(2) Are the killings of Palestinian civilians proportionate in relation to the aim of protecting Israeli soldiers?
These questions are distinct, for it is arguable that the standard of proportionality is more demanding in the second case. 

 It is true that the government of Israel has a duty to protect its civilian citizens, the vast majority of whom are not legitimate targets for Hamas fighters. Also the vast majority of Palestinians are not legitimate targets Israeli forces. The main issue is whether the killing of Palestinian civilians as a side effect is proportionate in relation to the threat to Israeli civilians that the invasion has been intended to eliminate.
" One can begin to understand the nature of proportionality by considering the morality of individual self-defence. Suppose your life is threatened by a culpable aggressor but your only effective means of defence will kill an innocent bystander as a side effect. Most philosophers believe that it would be impermissible to save yourself at the cost of killing this innocent person. This is mainly because the moral reason not to kill a person is stronger than the reason to save a person. It is therefore generally impermissible to kill one person to save another, even if the killing would be unintended. This is particularly clear in the case of third party defence of another person. Suppose, for example, that you are unable to defend yourself against the culpable aggressor but that an unrelated third party can defend you, though only at the cost of killing the innocent bystander. Virtually everyone agrees that it would be wrong for the third party to do this."
Some philosophers have argued, however, that self-defence is different from defence by a third party, in that when it is you who are under threat, you have what might be called a “self-preference permission” to give your life some degree of priority over that of another equally innocent person. Hence you may save your life by killing the innocent bystander as a side effect, even though a third party would not be permitted to save you at that cost. Even so, the priority that you are entitled to give to your own life is limited. While it may be permissible for you to kill one innocent bystander as a side effect of saving your life, it is probably not permissible to kill two, and certainly impermissible to kill three.
Next consider what third parties are permitted to do in defence of others. In general, a third party may cause no more harm to innocent bystanders in the course of defending another person than that person would be permitted to cause in defending himself. This is certainly true of third parties who are unrelated to the person they defend, and it is also true even of most third parties who are specially related to that person. If, for example, you hire a bodyguard to protect you, he would not be permitted to cause more harm to innocent bystanders in defending you than you would be permitted to cause them in defending yourself.
Some philosophers who claim that individuals are permitted to give a certain degree of priority to their own life also contend that this permission can be extended to certain others as well. These philosophers suggest, for example, that you can transfer your self-preference permission to your bodyguard, so that it becomes permissible for him to give your life the same priority that you are entitled to give it. But this is controversial. If individuals have a self-preference permission but it does not extend to others, it is then in general impermissible for third parties to cause as much harm to bystanders in defending others as those others would be permitted to cause in their own defence.
With these claims about the killing of innocent bystanders in mind, return now to the issue of proportionality in Gaza. The assumptions that are most favourable to the view that Israeli action has been proportionate are that individuals have a self-preference permission and that that permission extends to the soldiers who defend them. According to the first assumption, an Israeli civilian would be permitted to kill one or perhaps even two innocent bystanders if that were an unavoidable side effect of defending herself against a lethal threat. According to the second assumption, an Israeli soldier would be permitted to do the same—though no more—in the civilian’s defence.
" Suppose for the sake of argument that of the 1800 Palestinians killed so far by Israeli soldiers, a thousand have been civilian bystanders—probably a significant underestimate. Given the two assumptions just stated, these killings have been proportionate only if they were unavoidable side effects of action necessary to save at least 500 Israeli civilians. If we were also to take into account the number of Palestinians that have been seriously injured—which greatly exceeds the number that have been killed—the number of Israeli civilians saved would have to be even greater for the killings and injuries to be proportionate. Yet it is extremely unlikely that the invasion has prevented more than 500 Israeli civilians from being killed. Hamas’s rockets are in general small and inaccurate, while Israel’s anti-missile system is highly effective, which explains why virtually all of the several thousand rockets launched by Hamas have either been intercepted or landed in uninhabited areas. The tunnels are nothing more than means of individual entry into Israeli territory—an instance of the sort of physical vulnerability shared by every state that borders on another."
"Next consider the pair of assumptions I suggested are actually more plausible—namely, that individuals have no “self-preference” permission to kill an innocent bystander as a side effect of self-defence, and that third parties may cause no more harm to innocent bystanders in defending others than those others would be permitted to cause in their own defence. Given these assumptions, it would not be permissible for Israeli soldiers to kill two Palestinian civilians, or even a single Palestinian civilian, as a side effect of preventing the killing of one Israeli civilian. It might, of course, be permissible for them to kill a Palestinian civilian if that were an unavoidable side effect of saving some larger number of Israeli civilians. But assuming that the duty not to kill is stronger than the duty to save, the number of Israeli civilians that would be saved must presumably be greater than two. Suppose, for example, that a police officer could prevent two innocent people from being killed only by acting in a way that would kill one innocent bystander as a side effect. It is doubtful that it would be permissible for him to do this.But let us again make an assumption favourable to the proportionality of the Israeli military action—namely, that it is permissible for Israeli soldiers to kill one Palestinian civilian if that is an unavoidable side effect of saving two or more Israeli civilians. Again assuming that 1000 of the Palestinians killed by Israeli forces have been civilians, the invasion must have prevented the killing of over 2000 Israeli civilians to have been proportionate in the harm it has inflicted on Palestinian civilians thus far. For the reasons given earlier, that is highly implausible."
Some defenders of the invasion deny that those whom Israeli forces are killing are innocent bystanders and claim instead that they are legitimate targets. Rabbi David-Seth Kirshner, for example, president of the New York Board of Rabbis, recently addressed a cheering crowd of 10,000 people outside the UN with these words:
“When you are part of an election process that asks for a terrorist organisation which proclaims, in word and in deed, that their primary objective is to destroy their neighbouring country and not to build schools or commerce or jobs, you are complicit and you are not a civilian casualty. When you fail to heed the pamphlets, the phone calls, the text messages, and the warning shots [from the Israeli army] telling you to evacuate a building, and instead use yourself as a shield and use your innocent children as a shield, you are not collateral damage. When you ignore those very moral warnings and align yourself with Hamas, you are a combatant.”
It is reassuring when men of different faiths agree. In his 2002 “Letter to America,” Osama bin Laden also affirmed that voting is a basis of liability to be killed. He suggested that Americans might challenge the claim that they have done something that might
“justify aggression against civilians. [But] the American people are the ones who choose their government [and] have the ability and the choice to refuse the policies of the Government and even to change it if they want. … This is why the American people cannot be innocent of all the crimes committed by the Americans and Jews against us.”
The difference is that Kirshner’s view goes beyond bin Laden’s in recognising more numerous grounds for finding people morally liable to be killed. On his view, for example, an elderly Palestinian becomes liable to be killed if she chooses to be unable to afford a mobile phone, or chooses to be too ill to leave home, and thus dares Israeli forces to kill her by failing to heed their very moral warning that they are about to blow up her house.
No doubt there are some Palestinian civilians who have actively aided Hamas in smuggling in and storing rockets, or in building tunnels into Israel. If these particular civilians are harmed as a side effect during the effort to destroy the rockets and tunnels, they may have no legitimate complaint. But the vast majority of civilians in Gaza are neither terrorists nor terrorist supporters. They are normal human beings who would like to live normal lives, but are caught between the IDF, who will not let them leave Gaza, and Hamas militants, who use them as shields. Significantly fewer than half the Gazans who voted in 2006 voted for Hamas, and many of those did so for reasons of domestic policy, as Fatah and the PLO had become notoriously corrupt and incompetent. Approximately half the residents of Gaza are children, who are ineligible to vote.
 "For defensive killing to be permissible" argues Jeff, "it must be not only proportionate but also necessary, in the sense that there is no equally effective but less harmful way of achieving the defensive aim. In the present case, the question is whether the killings in Gaza are necessary to protect Israeli civilians from Hamas. The war is necessary for defence only if Israel continues to quarantine the citizens of Gaza and to occupy and maintain settlements in the West Bank. If Israel were to abandon the aim of controlling territories to which it has no right, and to respect the right of Palestinians to a fully self-determining life in the lands allotted to them in the UN settlement of 1948, those who now fire rockets into Israel and conduct raids on Israeli forces would lose what sway they now have over the Palestinian people. Ordinary Palestinians want what other people want: to live with dignity, free from domination and oppression by others, to be secure and self-determining, and thus to have the opportunity to flourish in their own way."