WHy do so many people think USA was dumb to bomb japan with atomic bombs?

i read all about the situation back in the day, and the japanese just woulnt call it a day so we had to either burn all of them alive with fire bombing, or else vaporize them with atomic bombs. SO president truman chose the option with least killed. this was the original concept of "shock and awe" --you demostrate utter detruction on a few, and the rest will submit. So, as i understand it, it was either invade japan and lose thousands of american marines, or else drop atomic bombs until they give up. wat do you think