Everyone is talking about the civilian casualties in Gaza and what Israel can do to minimise them. It seems obvious that killing civilians is something anyone should wish to avoid. However, for the benefit of the few who remain unconcerned with the death rate of civilians in Gaza, and because there is no harm in stating the case, I have decided to explicate some reasons why it is a bad thing for enemy non-combatants to die in conflict.
Simple morality: consider the isolated case of two people standing face to face, one having done nothing to provoke the other. All but the most depraved would agree that if the latter were to kill the former it would be unjustifiable and constitute murder. Morality does not fundamentally change in a war zone. Because civilians are not getting involved, it is plainly and grossly unfair for them to suffer, let alone be killed. Even if a civilian supports combatants, this is not justification for their death, unless their support is directly involved in killing (e.g. by providing weaponry) – and even then, lesser measures such as arrest should obviously be attempted first. If this is not clear, think about whether bringing pizza to an IDF battalion should allow Hamas to attack you.
The case of collateral damage is distinct only in terms of intent. It is akin to the difference between murder and manslaughter – the outcome is the same; only the intent differs. Essentially, all the nations have agreed that manslaughter will go unpunished in war, as long as there really was no alternative and the advantage and necessity of the action which led to it were sufficiently great. Even so, it fundamentally remains manslaughter.
Grievance among the living: thinking more strategically, when a civilian is killed, it will greatly aggrieve their relatives, friends and compatriots. It is highly plausible that some of these will attempt to seek revenge. The more deaths, the more hatred is created and the more Israel will face emotional opposition from Palestinians.
Rewarding people who don’t engage in conflict: this is an even longer term consideration. If people across the world know that they cannot be targeted if they avoid combat, they will prefer to remain peaceful for the sake of self-preservation. Over time, fewer people will engage in hostilities, and the world will become a more peaceful place. Additionally, some of the civilians might be avoiding conflict precisely because they oppose it; they might even side with Israel, or come to do so later in life. A civilian is a potential ally.
International opinion: more cynically, at the very least, everyone must agree that civilian casualties loses Israel support abroad and are thus undesirable.
Moral equivalency: intentionally killing non-combatants to achieve deterrence is terrorism and puts us on the same low moral plane as the very people we despise. Being callous and not caring whether civilians die is one level above that, but still ignoble and unworthy of an ethical human. The only decent position is wishing for civilians to come to no harm.