Civilian Bombing or Tactical Airstrikes?

While watching "People's Century" on Friday about civilian bombing, it was clear where the line was between military and civilian bombing (at least as clear as it can get). Bombing by both sides during WWII included heavy focus on non-military targets, heavily populated cities with no significant military value, to 'break the will to continue'. Here the line between the two was distinguishable, but since then it has become more and more unclear where military battles end and civilian bombing begins. In Vietnam forests were burned to the ground to chase out the enemy, in Korea the situation was very similar. And in Afghanistan NATO forces carry out 'strategic' air-strikes meant to pinpoint and destroy the enemy. But when the enemy is barely distinguishable and living amongst innocent people, is it civilian bombing? How does a military deal with an enemy who lives and blends in with civilians to deter attack? While it is true that NATO uses the most advanced weapons to make the most of each strike by killing the most amount of enemy, least amount of civilians, using the least amount of explosive, these strikes hardly leave the innocent untouched. We occasionally hear of air strikes missing a target and killing innocent Afghans, but what of the rest, the supposedly 'unharmed'?  Dropping 20,000 lbs of explosive will undoubtedly effect anyone living within a mile of the blast. The innocent population lives in fear and stress of the possibility of being bombed at any time, and ruled by insurgents. But if NATO troops were sent in, the situation could turn into a nightmare of not knowing enemy from civilian and going on a goose chase facing a higher death toll than bombing. So the question is, when does tactical bombing become civilian bombing if only insurgents are targeted?