The scripture does not leave any room for anyone to make an exception. Anyone who has ever gone into battle...for any reason whatsoever...is disobeying God's Word.
What about the ones who were specifically commanded by God?
1 Samuel 15:3 - "Now go, attack the Amalekites and totally destroy all that belongs to them. Do not spare them; put to death men and women, children and infants, cattle and sheep, camels and donkeys.’” 1 Samuel 15:18-19 - "And he sent you on a mission, saying, ‘Go and completely destroy those wicked people, the Amalekites; wage war against them until you have wiped them out.’ Why did you not obey the Lord? Why did you pounce on the plunder and do evil in the eyes of the Lord?”"
So not only was Saul commanded to kill, but he was actually reprimanded for not being more thorough in his destruction.
I understand that this is not supported by the 'whole of scripture', but how can you possibly maintain that God has never wanted anyone to kill anyone when the Bible has examples of Him specifically commanding t?