War should be controlled by rules, but the rules should be realistic. If some of the rules of war are unrealistic, countries' respect for even the more realistic ones will be diminished. They will feel that the rules of war are idealistic nonsense and will be less likely to obey them.
Because you are asking this about the Battle of Britain and the Blitz, I assume that you are asking about rules with regard to the bombing of civilians. During WWII, it would have made no sense to try to have rules prohibiting the bombing of civilians. Bomb technology (and bombsight technology) at that time was not advanced enough to allow bombing to be accurate enough to hit only militarily important targets in an urban area. Since such a rule would be unrealistic, it would not have made sense to have it.
So, in general, I do believe war should be governed by rules. There should be no killing or mistreatment of prisoners of war. There should be no use of chemical weapons. But the rules of war need to understand that war cannot be made "clean."
Maori controlled War by rules even more than the British. In fact at the battle of Gate Pa when British Imperials were defeated, there was a media cover up campaign to help save face. The problem was that everyone already knew since the campaigns had been going on for weeks and weeks.