The legitimate and legal (under international law and the articles of war) way is to weigh the military objective against the civilian damage and casualties and

The legitimate and legal (under international law and the articles of war) way is to weigh the military objective against the civilian damage and casualties and decide if this is still a viable target. E.g. it might be legitimate to flatten a house with one civilian and a hundred soldiers in it. It would be grossly out of proportion to kill a hundred civilians just to kill one soldier. Everything between those extremes will be decided by maybe a war crimes tribunal, public international opinion, the conscience of the warfaring parties, circumstances, propaganda, etc. And there is no possible comparison between the usual peace-time internal court system and international law and wartime law. Those work in completely different ways. International law and articles of war are basically only applicable if some party makes them applicable by force. E.g. if the victor or a sufficiently mighty third party creates a war-crimes tribunal. In all other cases, those are mere "guidelines".