I'm a liberal Israeli. The border used to be mostly open. With the Oslo accord the Hamas started bombing civilians (busses, coffee shops etc.).
The wall is a problem but it stopped this. Hamas did its best to destroy the peace that was forming. It found a collaborator in our PM (Netanyahu) who essentially supported them and elevated them so they will fight with the PLO.
The idea was that it would prevent the formation of a Palestinian state. That was always a stupid idea... Notice that this was never "official" policy, this is my interpretation based on his actions.
Right now the specific blockade is fulled by three things:
* Rage - this is something I feel personally as everyone lost someone they know there. It's a small country... When children are murdered it tends to bring out blind rage and indifference towards the other side.
* Fear - Israel survived in a very hostile environment thanks to its ability to instill fear in its enemies. This showed a weak underbelly and Israelis are rightly concerned that anything less than complete destruction of the enemy will trigger an all out war.
* Hostages - There are civilians and children held hostage. The minister responsible for infrastructure specifically said that electricity and water won't be restored until the hostages are returned.
I personally think the bombings are absolutely horrible. I know quite a few Palestinians and my heart goes out to them. There's a mob mentality on both sides and we both lack in leadership. It took 5 days for the MODERATE head of the PLO to issue a very weak condemnation of the attack. On our side Netanyahu is as corrupt as they come. A demagogue of the worst kind. He promised to "flatten Gaza" which is stupid. I don't want that.
The Hamas has been a cancer on the Palestinian people. It murdered more Palestinians than Israel ever did. They believe in holy war and that Palestinian dead will be rewarded in the afterlife. The death of a Palestinian child is just PR for these guys. They are as terrible as they come. Unfortunately, this cancer masticated through the population. I have no easy answered but one thing I think pretty much every Israeli agrees on, they MUST be destroyed completely. Not the Palestinian people, the Hamas. My main concern is the leadership vacuum. The PLO isn't great either and won't want to collaborate with Israel after everything it did... Going back to something resembling the Oslo accord will be hard on all fronts.