You failed to consider a combination. For instance, the main objective of the war is preventing terrorism, but the fact that the Taliban would have killed people if left in power changes it from “lots of lives lost to prevent terrorism” to “few lives lost to prevent terrorism”. Just because preventing the Taliban from killing wasn’t our main goal doesn’t mean that it can’t affect the balance in favor of the goal that we did have.
You failed to consider a combination. For instance, the main objective of the war is preventing terrorism, but the fact that the Taliban would have killed people if left in power changes it from “lots of lives lost to prevent terrorism” to “few lives lost to prevent terrorism”. Just because preventing the Taliban from killing wasn’t our main goal doesn’t mean that it can’t affect the balance in favor of the goal that we did have.