On the side of the Palestinian cause are arguments about Israel blocking access along the borders of Gaza, specifically Egypt and the Mediterranean, and the involvement of Israel in creating their enemy. Arab support is also along the lines of mutual ancestry, mutual religion and mutual hatred for Israel.
On the side of the Israel cause are arguments about right of defence, right of conquest, larger concessions in negotiations. This on the background of a repeated stated desire of their enemies to completely annihilate them. There is some support from some advocates of democracy because of Israel's political structure. Several Christians are sympathetic to Israel because of their eschatological beliefs.
Without discussing the merits of these arguments nor resolving the various rights of both parties, I wish to comment on the ethics of the warfare and tactics as it relates to this conflict. I will discuss proportionality here and civilian casualties in a later post.
A lot is being made of the proportionate response theory. The idea being that the defence against an aggressor is proportional to the attack. This appears to be analogous to the principle of talion. The difficulty here is that talion limits the punishment for a crime committed by an individual. Under this principle a murderer can be put to death but a assaulter cannot be. You can force a thief to recompense his victim (and fine him) but not cut off his hand.
The number of casualties in a war is the sum of all individual deaths. However the idea that total number of deaths is comparable does not automatically follow. Each individual has died, but the addition of one individual's death to another does not seem to make sense.
Granted, mass death seems more horrible than individual death, and it is. But even with a single death, that person has still died. If a serial murderer is put to death for his crimes, he is only executed once. It doesn't matter whether he killed 3 people or 27 in terms of the degree of his punishment. We don't go and find 26 of his acquaintances to execute to even the numbers.
One could argue that victim proportionality can be applied to warfare even if it cannot be applied to serial murder because an army has a chain of command. But war is also an act of the state, not of individuals; and it is to individuals that talion applies. Suffice to say that totalling deaths to assess "proportionality" lacks any convincing principle and appears simplistic.
I am not even certain that "proportionality" by any metric is a required ethical aim for warfare, as opposed to, say, the combatant/ civilian distinction.
But assuming proportionality, as so many do, a more rational approach to proportionality is to look at intent. If soldiers from 2 countries are fighting each other, the fact that 1 side is more successful in killing the other side just reflects their better ability. Both sides are continuing to fight. Where proportionality potentially comes into play is when 1 side surrenders. Significant ongoing warfare after surrender (and agreed terms of peace) could be argued as disproportionate. So if Hamas continues to fire rockets into Israel, even though Israel has killed more Palestinians than Hamas has killed Israelis, then the response by Israel can hardly be described as disproportionate.
Now it is important to note that Jesus was talking about joining the kingdom of heaven: men should consider all the implications of following Jesus. Jesus is not necessarily justifying some wars, nor is he commenting on the righteousness of the king's cause. But he is making an observation about kings that his hearers would have understood: when rulers know they cannot win they show prudence by negotiating.
Or what king, going out to encounter another king in war, will not sit down first and deliberate whether he is able with ten thousand to meet him who comes against him with twenty thousand?And if not, while the other is yet a great way off, he sends a delegation and asks for terms of peace. (Luke 14)
The principle of proportionality also allows the aggressor disproportionate positioning. The aggressor can attack at will and the response is dependant on the attacks. This allows the aggressor to optimise his position and fight as munitions become available, knowing they will never be attacked at a greater level than they inflict. If this is disputed then why do those who hold to proportionate response not ask the aggressor to cease fire then the response to cease? Note that with individuals the wrong is with the aggressor (if it is not then they are not punished) and a proportional punishment against him acts as a limit on further activity. With warfare the aggressor may not be in the wrong and even if they are a proportional retaliation does not limit further activity.
None of this states which party is morally right or wrong in the situation. There have been cases when the righteous have won battles and wars and cases when they have been defeated.