The question of how we trade off different methods of achieving broadly humanitarian ends is a different question than how we trade off broadly humanitarian ends against different ends. If the only case being made for the air strikes is humanitarian, then it makes sense to see if it's reasonable humanitarian bang for the buck. Of course, there are other ends that the air-strikes might serve, though I have no sufficiently informed opinion on their effectiveness (or counter-productiveness).
The question of how we trade off different methods of achieving broadly humanitarian ends is a different question than how we trade off broadly humanitarian ends against different ends. If the only case being made for the air strikes is humanitarian, then it makes sense to see if it's reasonable humanitarian bang for the buck. Of course, there are other ends that the air-strikes might serve, though I have no sufficiently informed opinion on their effectiveness (or counter-productiveness).