The issue is made complicated, however, by the broader front to delegitimize Hamas. The most important aspect of this has been the blockade of Gaza, a blockade which seems to stem from the same school of thought that inspired the sanctions to be put on Iraq and Cuba. Such sanctions have only ever worked if the entire international community was involved and if the society was internally stable and democratic enough that people would oust the offending government so as to improve their economic positions and cease being a rogue state. The sanctions regime actually strengthened the internal position of Saddam Hussein, and while Hamas is no Saddam, I suspect something similar is happening there as people become increasingly dependent on the source which controls the flows of wealth through society. By applying such severe restrictions to an entire population, Israel and Egypt are committing a crime against humanity compared to which Hamas's indiscriminate rocket fire is a misdemeanor.
One issue going forward if the effectiveness of Israel's campaign, both in weakening Hamas and in Israel's electoral campaign. Although I obviously have moral misgivings about war for political reasons, Joshua Mitnick's analogy to Operation Grapes of Wrath intrigues me. As a practical matter, had Peres won and signed a peace agreement, the region would be far better off today. Similarly, I'd much rather see Tzipi Livni as prime minister than Benjamin Netanyahu. What the different scenarios for Hamas's future might mean is much more clouded.
Finally, as the noted a few posts below, determining what makes a legitimate target is much murkier when the very government in a territory is held to be an illegitimate terrorist organization. In this context, Israel's proclivity for going for a broad definition is an obvious object of concern, and whatever the dubious merits of their campaign, which sooner or later will end in another truce, Israel will bear some responsibility if society collapses back into gang rule.