Israel's bombardment of Lebanon is most often criticized for being "disproportionate." Is this a legitimate complaint? Partly. Although the idea of proper "proportion" is simplistic, it can be valuable.
On strictly ideological grounds, the basis for proportionate response is flimsy. Crack it open: what's the underlying ethical principle, if not an archaic "eye for an eye" belief in just retaliation?
But despite the idea's lack of any cogent moral basis, it remains valuable in strategic terms. Proportionate reponse happens to be the optimal method of deterrence in many situations that lack an ideal resolution. For instance, Israel's broad assault on Lebanon in response to Hezbollah's aggression has weakened the nation's nascent democracy and fomented wider hatred. Israel is clearly incapable of destroying Hezbollah. Why not, then, a more measured retaliation to weaken the organization and demonstrate consequences for unacceptable behavior?