what part of 'an act of war' don't you understand?
countries dont go about qualifying various attacks into certain degrees and responding likewise. If you perform an act of war, whether it be the kidnapping of two soliders (and the killing of a number more) or bombing a city, expect to get into a war.
Israel's been remarkably restrained during this whole conflict. They have every right to roll over Lebanon completely, however they're wise enough to know they're best served in the long run by responding with restraint.
Over 14 days they've killed only about 3-400 people. They've struck targets which weakened Hezbollah.
Coincidentally, Lebanon itself wants Hezbollah gone, and even the surrounding nations like Saudi Arabia are stating that Israel's in the right