Why would the Israeli navy commandeer boats carrying collapsible wheelchairs and bags of cement to the Gaza Strip? Israel says that the aid convoys are trying to "break the blockade" of the densely populated Palestinian enclave. But why is there a blockade in the first place?

Sen. Chuck Schumer, an ardent supporter of Israel's policies, recently offered an unusually frank explanation before a Jewish audience in Washington. The siege of Gaza aims "to show the Palestinians that when there's some moderation and cooperation, they can have an economic advancement," the New York Democrat said. "To strangle them economically, until they see that's not the way to go, makes sense."

Israel and its defenders often claim this blockade is necessary for security reasons -- to prevent the importation of weapons, for example. In the wake of the disastrous May 31 raid on an aid flotilla, however, it has emerged that the list of prohibited items includes paper, notebooks, pens and fresh meat. What security purpose could a ban on pencils or ground lamb serve? Schumer's comments reveal that this is really a way to punish the people of Gaza for their political choices.

Israel's trying to make life so difficult for Gazans that they will somehow get rid of Hamas, the Islamic resistance movement they helped elect to lead the Palestinian Authority in 2006. Israel tacitly acknowledged that the blockade is political when it bowed to international pressure and lifted some of the restrictions. Blocking Gaza's legitimate trade violates international law. Collective punishment is barred under the Geneva Convention, which, as the occupying power, Israel is bound to uphold in Gaza.

Even on Israel's own terms, the attempted economic strangulation doesn't make sense.

Such sanctions generally don't work. Years of sanctions didn't topple Saddam Hussein, for example. In Gaza, the Israeli-imposed isolation hasn't made a dent in Hamas' control, which has only grown in the years since the blockade was imposed. In fact, it has provided Hamas with extra revenue: The governing party is collecting taxes on goods smuggled through underground tunnels straddling the Egypt-Gaza border.

After three years of siege and a three-week bombardment during the winter of 2008-2009, from which Gazans have been unable to rebuild due to restrictions on the importation of building materials, Gaza is completely devastated. Sixty-five percent of children between nine and 12 months old are anemic. Since Israel's winter assault, Gazans have lost access to 46 percent of their agricultural land -- either because of the destruction caused by the Israeli bombardment or because Israel does not permit them to cultivate land labeled a "buffer zone." Many fishermen in this coastal territory have lost their livelihoods, as the area in which they are permitted to fish is greatly limited and they frequently come under fire from Israeli patrols.

Allowing more humanitarian supplies to enter Gaza will ease the misery, but it won't solve the problem, which can only be accomplished by completely lifting the blockade. Gaza is tiny, approximately the size of Chicago. Two thirds of its population are refugees who either fled or were expelled from their homes during the war that led to Israel's founding in 1948.

For a territory so small and so densely populated, trade is essential to the economy. Gaza needs to be able to export manufactured goods, and its youth need to seek educational opportunities abroad. Its residents have personal and business interests outside of this tiny area, but under the siege they have been unable to travel for work, for school, or to visit family. Without a complete lifting of the siege, Gaza will be perpetually dependent on international handouts.

After three years, it should be clear that Gazans cannot be starved into submission. Isolation doesn't engender tolerance, and peace without justice is unsustainable. The siege is a failed political strategy and an injustice for the 1.5 million Gazans who are denied freedom and opportunity. Easing the blockade would mark a step in the right direction, but it's long past time to lift the siege entirely.