Ezra, who's written a bunch of sensible stuff on the Gaza bombings, says that people keep asking: "What would you have Israel do in response to non-lethal rocketry?" Hamas, after all, didn't kill a lot of Israelis with the rocket attacks that got the Israelis killing hundreds of people. All the casualty counts I've heard from Hamas rockets have been in the single digits, with most of that coming after Israel started bombing.
If I had to think of a proportional response, it'd probably be dropping a bunch of bombs on some relatively uninhabited part of Palestine where there aren't any people. This, of course, would be annoying and bad, just as the Hamas decision to shoot rockets at Israel that don't kill anyone is annoying and bad. But it wouldn't be as bad as killing hundreds of people.
Thinking you can destroy Hamas by bombing hundreds of people is like thinking you can destroy the Democratic Party by killing a bunch of Democrats. The political institution will live on, and attract popular sympathy because of its members' martyrdom.