Juan Cole:

The Israelis already have the Gaza Strip under military siege, carefully controlling what and who goes in and out of it. They have now cut off most fuel, and the United Nations has been forced to stop distributing food aid.

This Israeli government action is an unvarnished war crime. It is known as collective punishment. There was already hunger and malnutrition among Palestinian children, which will now be worsened. ...

Cutting off fuel to the Gazans and provoking a cut-off of UN food aid is not only criminal but also stupid. It is difficult to imagine such mean-spirited sanctions against civilians having any policy effect whatsoever, so they are just making Israel look bad.

The Israeli argument is that they need to employ collective punishment to stop the rockets being fired on Sderot. That would only be a legitimate argument if it had any chance of working. But it doesn't. What is will do, besides killing children, is further harden the support for Hamas, as the only viable tactic available. Morally, the number of people that could die in a siege far outweighs the few killed by the rockets; not to mention the people who die slow deaths by malnutrition, absolute poverty, lack of health care, etc; so it's hard to see how Israel has the moral high ground here.
As with so many of Israel's policies, I am left to wonder: where is the wisdom? What's the end game?
(By the way, those who argue that this is all the fault of the disengagement conveniently forget that Israeli soldiers and civilians were being killed on a regular basis in Gaza during the occupation there. I doubt many IDF soldiers regret the withdrawal.)