That's where you go wrong - you see the nuclear bombing of Japan as an isolated event. Place it into the context of several hundred thousand people dying every month as it was at the time, and it will look different.
I would also argue that the use of those bombs saved many more lives by teaching the world a lesson about the horror of nuclear weapons. Its very possible that nuclear weapons would have been used in future conflicts when they would have been much more prevalent had it not been for the example set in WWII.
Japan didn’t even surrender after the first one! It took two to convince them it wasn’t a one-time fluke and that it was real and could be repeated.