One of more maligned films in the Jewish world in recent memory was Munich. Munich told the story of the aftermath of the massacre at the Munich Olympics. As everyone is well aware, Israel recruited a team of assassins to kill the members of the Black September who plotted the massacre. The movie takes a number of liberties with the facts and is designed to get across the moral difficulties inherent in such forms of retaliation.
At the end of the movie the protagonist Avner, no longer the cockeyed idealist at the start of the movie, poignantly asks his handler what was gained from killing these men; after all they were quickly replaced. To which his handler responds "why cut my fingernails? They'll only grow back."
That's what Israel is essentially doing in this war. Israel cannot wipe out Hamas. Right now there is no other group that is capable of controlling Gaza and Israel has no interest in returning to Gaza. But Hamas was getting too powerful and was shooting too many rockets into Israel. So Israel decided to weaken Hamas so it would have a short respite until the next round comes in a few years. These are the realities of the Middle East where conflicts do not lend themselves to easy solutions.
That said, I don't understand what Israel intends to gain by launching this ground incursion. The loss of life and suffering on both sides (but especially in Gaza) that resulted from the ground operation cannot be justified if the sole gain is to weaken Hamas. Hamas was already greatly weakened by Israel's aerial campaign, and it seems to me that the utility of the ground campaign is outweighed by the substantial human cost. But I guess other people could have a different calculus.