OK, Israel has a right to respond to missle attacks. That’s a very small part of the story you posted. It’s mostly about the violence in Gaza and the refugees.
As for the violence in Gaza: Israel and the U.S. most definitely played a role and inflamed it. Bush babbled on about elections and democracy, and then when Hamas won legal and legitimate elections, Bush and Israel did everything they could to deny Hamas' election victory - including arming the losers of the election: Fatah. When you try to meddle in an election, and then arm the election losers, that's going to piss people off. That doesn't mean I'm a fan of Hamas. That's just a fact. Hamas are assholes. But, it’s not my country.
Bush told Arabs to lay down their guns and hold elections. Hamas said “Okay”, and did. Hamas won the elections. Then Bush armed and funded the groups that lost, to decapitate the victors, Hamas. This is stupid. It makes us look like hypocrites and liars. This american policy simply doesn’t work, and makes things worse.