Israel v.s. Palestinian casualty discrepancy? 4 v.s. 400?

You're confusing war with games. There's no reason to compare casualty numbers. Hamas have been shooting thousands of rockets and mortar rounds into Israel for years, and the fact that they don't kill too many people is not an argument. What you're missing is that you're thinking reasonable people would compromise to gain a peaceful resolution. Hamas are not reasonable and will not negotiate a peace, so there's little alternative for the Israelis. Indeed, Hamas policy is to continue to the last drop of their neighbors' blood, and their military positions are designed to maximize civilian casualties. The 400 number is by Palestinian, not Israeli, design. The Israelis were, in fact, sending flyers asking for civilians to remove themselves from targeted areas before they were bombed, and Hamas were discouraging evacuation. One might think that the Palestinians of the Gaza strip would prefer live children to dead martyrs, but so far that hasn't been their thinking, else they'd have thrown off the yoke of Hamas.