An interesting question.
Hamas was elected by the people of Gaza to run its government. Israel believes that Hamas is a threat to its continued existence. It no doubt has good reasons for believing that. In light of this perceived threat, Israel waged a brief but very bloody war against Gaza last year, killing 1400 Palestinian civilians. Since Hamas won the election in 2005, Israel has blockaded Gaza and has controlled what sorts of goods will be allowed in. Israel believes itself to be justified by the threat Hamas constitutes and, all in all, the United States government -- whether under Bush or Obama -- agrees.
But now consider this analogy. Presidents Bush and Obama have been elected by the American people. Osama bin Laden believes that the US is a real threat to the Mideast, to Arab countries, their ways of running their lives, their values and their religion. There are good reasons to think that Osama bin Laden is right about the threat we constitute to his, conservative, views about Islamic culture and the role of the US in the Mideast. Israel believing that Hamas is a threat uses massive violence to try to unseat Hamas. Osama bin Laden, believing that the US is a threat, uses spectacular violence to try to undermine American power.
If those two actions are roughly parallel, why is Osama bin Laden a terrorist and the object of a seven-year manhunt while we support Israel with $3 billion a year of military aid?