The fire bombings of Japanese cities was only incidental as the policy of total war by a non-stop air campaign designed to not only to destroy the ability of a nation state to conduct war, but to diminish their will to resist as well based upon a strategy that had been well developed at the time. That the policy was flawed is truly immaterial given that the decisions were predicated upon beliefs held at the time.
The theorem of Douhet and others that bombing civilians would break the population's will and that the 'bomber would always get through' originated shortly before WW1 and was elaborated on post WW1/pre WW2. The Germans experimented with it in the Spanish Civil war (Guernica) and were the first to put it prominently to the test vs. London and Coventry, though the theory was also embraced by the British.
The British, being on the receiving end first and thus being able to observe first hand that such bombings appeared not to break the will of the population but rather to increase their determination and resolve, were in the best position to at least question the theorem early in the war. After trying their own hand vs. the Germans, they should have and, in fact, did realize that large scale bombing of civilians would not break the will of the enemy population throughout 1943 at the latest, i.e. that the strategy was a failure.
Nevertheless, they carried on regardless, as did the Americans (as would have the Germans if they had had the capability for that matter). The important point is, however, that the beliefs held before WW2 and during its early years
had been proved wrong by mid war and
before most wanton destruction on civilians was wreaked. Thus, there was no excuse to carry on without a change of tactics, but this was exactly what happened. On the contrary, tactics on how to destroy cities (not merely their industries) were refined after it had been discovered on how to bring about firestorms in Hamburg. Indiscriminate killing of civilians and the destruction of their livelyhood was precisely the objective despite it was realized at the time that would not bring about the desired effect. Eventually, especially the Americans began to systematically to target the fuel production, refineries, etc. which did more harm to the German war effort that destroying residential areas on a large scale. Yet, when they had destroyed everything of significant strategic value, they kept on destroying (by now mid-size) city after city simply because there was nothing else to keep the bomber fleets busy with.
Yes - the Germans did it first. Yes - the Allies believed that the strategy would work in the early years of WW2. And yes - the Germans would not have acted differently had they had the ability to do so. But after the realization at the time that the policy was flawed at the latest, to carry on and to refine it can only be described with the terms of 'war crime' and 'atrocity' - regardless of who would perpetrate it under these circumstances.
von Marwitz