I won't take position to a discussion based on Hiroshima, but here are my redundant, but really impartial (I'm neither fan of the two mentioned forces, nor any which participated on the WWII) 2cents:
I think every use of an atomic bomb is naive. It's not only an explosion, it's radio-activity (which causes sub-molecular damages, which are irreparable to us, idependently of its half-life, btw) which can be transfered over the sea & atmosphere to reach the whole globe. And then there are dangers even untold. These past actions had distant (yes, a "foe which can defend himself" than people which were strict persecuted) similarity to a genocide, which took place in my homeland. I guess a navy blockade and bombards on military installation would have brought the Japanese Emperor to the conclusion to capitulate his military to the allied forces. Of course, that would hunger the population, but unrest would also occure, which could have agitated against the regime. Ok, stupid rant, it had all to do with timing in the whole war, right? But I think the a-bombs were big 2 faults in the war - not only of the humanistic/medical aspects and a cultural/psychological shock (the second wave of memetic kind followed and was also extremelly), because of the human ignorance of wielding with not understood powers towards natural enviroment.
Even without any ecological grasp or ideology, it must be known that earth provides our lives for existance (more or less). That could wrote everybody, actually. But why can't react anyone of those powerful ones properly with such problems - economy can only function fluently if natural resources were offered - don't be a clueless hippie, think at least with a pragmatic spirit, if it is your only drive. I think our whole civilisatory system had a flawed initiation, therefore it was inevitably that everything developed to that state of today. Jep, that must be the simple reason.