In war civilians get killed, period. Israel as opposed to Hezbollah does not target civilians. Hezbollah does not care about civilians one whit and therefore places arms, people etc. specifically in civilian areas.
The reason for bombing the airport, bridges, roads etc. is twofold.
1. They want to make it hard for Hizbullah to move around (including moving the captured soldiers)
2. That same infrastructure was/is being used to bring in more weapons to Hezbollah.
This makes the infrastructure a perfectly legitimate military target.
This is more or less my view. I don't think Israel should deliberately target civilians under any circumstances, but during the current war with Hezbollah, I also don't think the IDF needs to be especially concerned about things like collateral damage, nor do they have to cross every T and dot every I before ordering a strike.
I make a distinction between the war against Hezbollah and, say, the Intafada. When the IDF operates in areas conquered in '67, Israel has responsibilities and worries that do not apply when a war is being waged against a foreign power.
Why? Because when Israel vanquished Egypt, Jordan and Syria in 1967 over 1 million Arabs became residents of Israel. I can tolerate some collective punishment and some presumption of guilt when you're waging a war against another country, but your own residents deserve better.