It's not about being behind Hamas. Hamas didn't come into being in a vacuum, but is a direct result of what was happening in the region for years. At first Israel let Hamas form or even encouraged it, attempting to use it to keep Palestine divided. Destroying Hamas, which has the highest cost for civilians, is useless if the circumstances that gave rise to it didn't change. Another Hamas will just form. It's like the US trying to bomb Taliban out of existence, they are in power now after all the death and tragedy.

Edit: if you want to know more, there's an archived Wall Street Journal article citing Israeli sources about how Hamas was formed, and the role Israel played in that.