Hmm, well i guess you need to look at the ends here.
Japan, they're one of the world powers and have a very strong economy...no? And how did they get there? US, WE BUILT THEM! They're now able to help millions in poorer countries, and without us they'd be nowhere near what they are today.
So do the means justify the ends? I'd say more good has come of it than not. Also, that allowed us to stop worrying about japan, and stop the nazis. Otherwise, hitler may have developed other weapons while we were fighting the japs, tortured more ethnic groups, etc.