ISRAEL has taken the fateful step of a ground offensive in the Gaza Strip because ultimately the threat it faces from Hamas is strategic, even existential.
Hamas has fired more than 6000 mostly Qassam rockets into Israel over the past four years.
They have killed only about two dozen people, although in other acts of terrorism Hamas has killed hundreds of Israelis.
But Israel must stop, or greatly reduce, the rockets from Gaza. It is an absolute strategic necessity.
Perhaps the stupidest line of analysis to emerge in recent days has been to compare the deaths from Hamas rockets in Israel to traffic fatalities and say that Israel should relax.
To grasp the nature of the strategic threat Hamas poses, it is necessary to place it in the context of its ally, Hezbollah, in southern Lebanon, and their common backer and puppet master, Iran.
During Israel's 2006 war with Hezbollah, rockets continued to rain down on Israel as far as the big industrial city of Haifa. There was an acute fear within Israel, although not much spoken of, that Hezbollah rockets would hit a massive oil refinery in Haifa. The flow-on effects from this could be catastrophic. During that war, much of northern Israel was effectively paralysed, and certainly closed for normal business.
Despite the mistakes Israel made in that war, it got some things right. At the start of the conflict, it knocked out Hezbollah's longest-range missiles that could reach Israel's biggest city, Tel Aviv.
And since then, the missiles have not come back from the north.
Now they come from Gaza in the south. They not only terrorise the small Israeli town of Sderot, they frequently now reach Ashkelon, the industrial city that ironically provides electricity to Gaza. (There must be few occasions in history when a nation is expected to supply electricity to factories building rockets designed to blow up the electricity plant.)
There are also chemical plants in Ashkelon that could be hit.
The rockets also reach Ashdod, Israel's biggest port. And they reach Beersheba, site of the famous Australian victory over the Ottoman Turks, and Israel's biggest southern city.
Nearby is Dimona, Israel's nuclear reactor and, apparently, the site of some of its nuclear warheads.
At the moment, Hamas does not have rockets of sufficient range and accuracy to hit any of these targets reliably. Apart from the Qassams, it uses Chinese-made Grad missiles and Katyushas, and some longer-range Iranian-supplied Fajr missiles.
Because it is hemmed in by Israel on one side and Egypt on the other, it has not acquired an arsenal as deadly or as large as Hezbollah's. But over the past 18 months, Hamas and Hezbollah have significantly deepened their military integration into the Iranian Revolutionary Guards.
Hamas leaders have been sent to southern Lebanon, as well as to Iran itself, for training by Iranians. And there are reliable reports of some Iranians getting into Gaza.
Hamas is recognised by the UN as a terrorist organisation. It is a branch of the Muslim Brotherhood. Apart from its repeated and blood-curdlingly clear rhetoric, the Hamas Charter shows that it has no negotiable aims. It wants the destruction of Israel and the death of the Jews.
Although a gruesomely extreme organisation, it does command significant popular support among Palestinians. However, it really won its one big election victory because it was seen to be, unlike Fatah, not irredeemably corrupt and because, like a number of sophisticated terrorist movements, it ran some social welfare activities effectively.
In the past year or two, however, it has transformed itself into a terrorist army. Hamas and Hezbollah are both grassroots popular movements. They are also both arms of state power, mainly Iranian but also Syrian.
They perform a superb function for Iran. Whenever Iran wants, it can strike in deadly fashion against Israel.
But Tehran has a level of deniability and official distance and therefore will not be subject itself to retaliation. The Palestinian people suffer the most from these cynical calculations.
From Israel's point of view, it is very clear that if it leaves Hamas alone, Hamas will gather more and better rockets, long-range and with better guidance systems.
Hamas and Hezbollah together can then present two types of strategic threat to Israel, beyond merely killing its citizens. They can shut down vast swaths of Israeli society and industry with a rocket offensive. Or they can hit strategic targets, at least from Dimona to Haifa.
Israel had no alternative but to act, although how it will restore a future equilibrium in Gaza remains deeply unclear.
