This isn’t a black and white moral issue in which something can be declared “justified” or “unjustified” and that’s the end of the matter.
The razing of cities has been seen as just and unjust by various people over human history. However, if the razing of axis cities has been conducted in the old fashioned way, by killing men women and children with hand held weapons, instead of bombs dropped from a distance, then the ≈650,000 deaths that resulted might be viewed differently.