I will agree that Gaza is unique. The entire region all 360 Square KM is basically a residential area with a few spots the size of a small town park being called rural. Any munitions that have a blast radius of over 10 feet will endanger non-combatants. does one go into such a region with massive fire power unless the primary intent is to kill the entire population.
Now, let us look at the "Danger" the Qassam and Katyusha rockets posed:
The range is very limited. The qassams are home made and not much more than sky rockets in metal skins. The range I believe is no more than 1 KM. The katyushas although antiques do pose a greater danger the most modern Katyusha has a range of almost 4 miles. It seems the most humane action Israel could have taken would have been to declare a buffer zone extending 5 miles out from the Gaza border and outlaw the building of residences in that area. this would have rendered any rockets from Gaza useless.
I know it would be unfair to ask some Jewish settlers to move out of their homes. But what happened to the Palestinians that got kicked out of their homes in 1948 and forced to go to Gaza, is fair..
My point being Israel had options to disable the threat without needing to level Gaza.