I also 100% totally agree that it was necessary to demonstrate the nuclear bomb in order to end WWII, esp considering that a number of other players were racing to do the same thing.
That does not at all mean that it was necessary to drop it on a peaceful city. They could have, for example, targeted the Japanese leadership -- altho this would probably involve an equal number of casualties, it at least might have killed some people responsible for the travesty in China, or even Pearl Harbour, etc. Which that was not anyone in Hiroshima.
Instead, the American leadership decided that targeting heads of state, or other generals, was out of bounds. Ie, we won't really hurt each other, we will just hurt our subjects and citizens. Very honorable! More like the exact equivalent of "cowardly terrorist attacks".