israel will roflstomp anyone who threatens them, for good or bad. I wish they would all just chill out and smoke some hashish.
If there is any country that has a position that has a justifiable position for such behaviour, it is Israel. A country surrounded by rather aggressive theocratic or autocratic countries, multiple of which have explicitly stated that they seek the destruction of the state of Israel with one of them actively trying to acquire nuclear weapons.
As far as Hamas is concerned, they have the legitimacy of a stone and are terrorist scum. PLO is a bit of a different case, but Hamas should get its ass kicked. I don't think actions like these by Hamas have enough popular support from any of the neighbouring countries to warrant violent intervention. Apart from that most of the neighbouring countries are in shambles anyway due to current or past revolutions. Don't expect anything big happening here apart from ye old condemnations.
Something big will happen however if Iran actually gives Israel enough reason to think they can build an atomic bomb. Cause with Ahmadinejad leaving very little doubt about his intentions for Israel, Israel will pull of another pre-emptive strike. Which will probably escalate in a full Israel-Iran war, which will bring the entire Arab League in there. Then the international scene jumps in, but probably very slowly. Israel might get another miracle victory, but if they start losing they also might chuck one of those atomic bombs they are not supposed to haven. That is when we enter World War 3, so someone better stop Ahmadinejad before Israel will have to.