The author of this piece addresses some of your questions Keith and comes up with the correct answer:

'We can say that there is a principle worth fighting and dying for: Civilians cannot be used to make just wars impossible and morality will not be used as a tool to disarm. And once we have that principle, the proportionality calculation changes. The deaths of innocents are not simply outweighed by Israelis' right to live without daily rockets and terrorists tunneling into a kibbutz playground; but by the defense of a world in which terrorists cannot use morality to achieve victory over those who try to fight morally. It is the protection of that world, one in which moral soldiers still have a fighting chance, that justifies Israel's operations against Hamas today. And it is that greater cause that decisively outweighs the terrible toll in innocent life.'

New Republic