If you are talking about massive, needless bloodshed then what about
1.2 milion people killed in Iraq? And why they were killed... to trial and execute
one man, and seriously don't tell me that Bush really believed him to be Ibn Laden's ally or that he wanted to bring democracy to the Iraq. Also I don't know if you heard that Husain was at the beginning US agent and US bring him to power.
Also one of the reasons why iraqis hate US soldiers so much is becouse they are ultra arogant and they don't give a damn about local customs and traditions. They believe that US culture and style of life is the best in the world and all others are crap that should be americanized. That is the biggest reason why even civilians oppose them, they hate people who came from distant country and tell them what to do and how to live. And don't tell me those are lies becouse I meet polish soldiers who were in Iraq and they told me how US soldiers behave. They often prefer to bomb bildings rather than search them, no matter if they are civilian homes or not (or even if there are people inside). Later they report that they killed "terrorists".
And to the Hiroshima thing, I'm just too lazy to write much myself so I checked the net, it took me one google search to find tons of opinions alike to mine and that's one of them:
The Hiroshima Myth by John V. Denson
Most (crushing majority) non american WW II specialists agree on that, it's a shame that most US citizens don't.