During wwII both England and Germany indiscriminately bombed civilians on both sides. We didn't have smart bombs to target military installations. We had to carpet bomb an area and hope we hit something.
That being said it's much different firing rockets when you don't have a hope in hell of winning the war. Then your just doing it to kill people not as a means to destroy an enemy or to win a war. Israel would be justified to cut off gaza completely. Allow anyone who wants to leave, leave without arms but not allow anyone to renenter the area. No food, no water, no power, no nothing.
I noticed a problem with the US's way of doing things that are alot alike how Israels way of doing things. They are both unwilling to do what it takes to win. Even when it's within their ability to do so.