Israel as the occupying power of the Gaza Strip has both an obligation and duty to protect civilians under its occupation. Since Gaza is not a sovereign state, Israel can not simultaneously occupy a territory and declare war upon it.War is not a game of proportional actions. War objectives are to win and bring the opponents to some submission or willingness to compromise in some negotiated peace deal.
Gaza was finally brought to some negotiated deal in exchange of a ceasefire. It has taken years to bring hamas to any formal compromise, even short term. We will see how long hamas can go without breaking the ceasefire. Till now hamas was unwilling to compromise, only to make wide sweeping demands before they would recognize Israel or to talk with them. They wanted to sweep Israel and it's people off the face of the map and occupy Israel.
Hamas is not even a member of the PLO, they have no real standing as a representative of the palestinians people. They control gaza by force. They were waging war on Israel forcing it to respond.
Jews want all the land between the River and the sea for a Jewish state with no more than 20% of its citizens being non-Jews; that's called ethnic cleansing anywhere except Palestine.
Israel must end its occupation of Palestine before peace between Jew and Arab has the slightest chance of becoming real, and we both know how unlikely that is.