Saw this for the first time last night - I'd seen Grave of the Fireflies and watched documentaries on Hiroshima years back, but this hit my a lot harder than I'd expected it to and probably one of the hardest things I've ever watched.
I disagree with the dropping of the bomb. It's not just the fact that this would involve more civilians than Pearl Harbour (and as others have said, military casualties are expected and accepted as part of war) - I think it was something like 4 or 5 times more civilian casualties than than military after Hiroshima. It's the sheer suffering. I'm not saying that getting blown up from the impact of a doodle bug or being gunned down or firebombed isn't horrific, but the appalling injuries, mutations, contamination and psychological impact (for example, the fear of the unknown and unexperienced - not understanding the black rain, why people are getting sick from radiation), not to mention the long-term health effects....that's something else entirely. I consider it to be a crime against humanity.
From my understanding, Japan were losing anyway but perhaps it was all looking a bit too expensive for the Allies to conduct a land invasion (even though they'd spent something like 2 billion developing the bomb), although I believe Japan should have surrendered after Hiroshima without question so in my view, they aren't without blame, and the UK authorised the attack. What angers me is the censorship and propaganda that was conducted afterwards, shielding the public from reality.
There are sources that claim the US dropped millions of leaflets to civilians in several cities (although not specifically mentioning atomic weapons to Hiroshima civilians) before they dropped both bombs, but, as they say, the victors of war write the history... It looks as though leaflets specifically mentioning nuclear weapons were dropped on Nagasaki and advising civilians to look to Hiroshima for an idea of the devastation, but how much the public knew and understood about what had happened days earlier in Hiroshima was very likely to be limited and after all, this was the world's first (and I hope last) experience of a nuclear attack.
Had Hiroshima been properly warned, perhaps it would have been largely evacuated first so the US's message to surrender wouldn't have had quite so much impact, but Hiroshima was a strategic target so at least some of their objective would presumably have been met by obliterating the infrastructure and contaminating the land, and at this point they wouldn't have known that Japan wouldn't surrender. The US had a load more bombs lined up for the coming months anyway so could have always upped the ante so I still believe it was way too heavy-handed.