Killing an individual is a bad act, period. Does an eye, substitute an eye ? I am not sure. Was the US invasion of Afghanistan justified - yes, definitely. Was the invasion of Iraq justified - it sure did in 2003, now it seems more tenuous. Increasingly, collateral damages seems unjustifiable, in any conflict. Not matter how good the intentions of an occupying army are towards civilians, collateral damage does occur and manifests itself in the deaths of thousands of innocent people - kids and women included. Maybe mankind should revert to the ancient war tactics that are described in great detail in the Indian epics.
Huge armies faced each other in large battlefields and fought to death. Children and women were not involved, crops would not be destroyed, cities would not be burned down - effectively, there would be no collateral damage. The world would probably be a happy place.