I talk in more (somewhat ramble-y) detail here [0], but I think I can put a more succinct version of the anti argument here, the main argument is that to morally justify the extreme act dropping atomic bombs on those cities requires an extreme set of justifications to the level of "it was the only option short of a bloody millions dead between both sides home island invasion" that history doesn't necessarily support.

The core thrust that undermines the this or that between bombs and traditional invasion justification for dropping the bombs is that a) the Emperor was already exploring possible peace deals and b) ultimately the Emperor was able to override the extreme militarists in the war council and accept the peace after the bombs. A lot of the pro-moral-bomb argument presupposes that the shock and awe of the atomic bombs were a prerequisite for the change in stance and that anything short of a full invasion of the home islands would not achieve shift large enough to get to a peace deal. (and that to achieve that impact required them to be used on a city)

Ultimately I think (and I know this is extremely hard to prove ahistorically) a naval blockade and shelling/arial campaign that devastated what little military might Japan had left would have lead to the same shift as the bombs and that the casualties from that would be lower or at least less morally weighted as the intentional atomic bombing of Hiroshima and Nagasaki. When that shift would happen and how to weigh the deaths morally are going to vary a lot from person to person though and I accept that.

> Even after all this, hardline military officers attempted a violent military coup to destroy the Emperor's recorded surrender broadcast and keep the war going.

A coup that ultimately fails though. I don't think anyone really argues that there weren't fanatical elements remaining even after the bombs were dropped. Their existence doesn't mean peace required the bombs however, the big question is what were the conditions that would reduce their power to the point the peace could be accepted. We have one example in the bombing but that doesn't mean that was the only option.

[0] https://news.ycombinator.com/item?id=49757977

I personally subscribe to the theory that nuking Japan (at least once) probably stopped the need for an invasion. Almost all of the archives that were sifted through pretty much answers the fact that the Japanese were never going to negotiate a peace that removed its militant aspects otherwise. There would likely have been another war and Japan wouldn't have become democratic.

The 2nd bomb? I can be convinced either way. Japan needed to know they had more than one, but it probably didn't have to be a city. That being said, this is a lot of presentism (looking at the past with modern ethics). World War Two was a brutal, total war and the long term effects of nuclear weapons were not fully understood. Remember that there was carpet bombing with incendiary bombs happening against Japan's wooden cities for the year leading up to this. A non-nuclear end the the war would almost certainly have involved a land invasion and many, many more deaths on all sides.

Japan (as a country) was also not innocent in all this. They started the war - both with China and the USA. The Japanese military IN COLD BLOOD slaughtered more civilians than the Allies did in all their strategic bombings, let alone just nuclear. Even the nuclear bombs had military targets in mind...

>...Ultimately I think (and I know this is extremely hard to prove ahistorically) a naval blockade and shelling/arial campaign that devastated what little military might Japan had left would have lead to the same shift as the bombs and that the casualties from that would be lower or at least less morally weighted as the intentional atomic bombing of Hiroshima and Nagasaki.

A full blockade would have led to many more deaths due to famine, etc.

The last major battle before the dropping of the atomic bombs was the battle for Okinawa and it was the bloodiest and fiercest battle fought against the Japanese. Absolutely no one who knew about that battle would have claimed that Japan was already defeated.

>...When the guns fell silent, more than 240,000 people had lost their lives in the campaign for Okinawa. The American loss rate was 35 percent of the force, totaling 49,151 casualties.

>...So close to the home islands, most Japanese soldiers refused to surrender and fought to the death. Their fanaticism contributed to a dreadful toll. Some 110,000 Japanese and conscripted Okinawan defenders were killed in action.

https://www.nationalww2museum.org/war/articles/okinawa-costs...

Japan had every intention of defending the main islands just as strong, or stronger, starting with operation Ketsu-Go. One of the slogans in Japan in 1945 was "The sooner the Americans come, the better...One hundred million die proudly."

https://irp.fas.org/eprint/arens/chap4.htm

The proposed allied invasion was planned to have 42 aircraft carriers, 24 battleships, and 400 destroyers and destroyer escorts. Please take a moment to try and picture that armada... Yet even with an armada of that size, that wasn't considered enough!

>...Ken Nichols, the District Engineer of the Manhattan Engineer District, wrote that at the beginning of August 1945, "[p]lanning for the invasion of the main Japanese home islands had reached its final stages, and if the landings actually took place, we might supply about fifteen atomic bombs to support the troops."

https://en.wikipedia.org/wiki/Operation_Downfall

One thing they would have been facing was a massive kamikaze force:

>...Estimates of how many would have been available vary, but range between 5,000 and 7,000; plans for waves of 1,000 planes were in place. Both sides planned for higher-than-normal success rates since the invasion would greatly reduce problems of finding targets ("fly to the shore, hang a right, find a transport") and the vulnerable transports would be concentrated near shore in order to offload troops. These weren't the only suicide attackers. The navy had midget submarines and frogmen who would attack the landing craft with explosive charges. Civilians were formally "drafted" into defense units, most of which had no military weapons or uniform, and which had been instructed to attack with bamboo spears or hand tools. There's no way to tell whether such units would have had any positive effect - but their inclusion would almost guarantee that US troops would fire on civilians, with the potential for mass slaughter.

https://www.reddit.com/r/AskHistorians/comments/4ka1z1/what_...

A Japanese military officer summed up the thinking by the Japanese military this way:

>...We will prepare 10,000 planes to meet the landing of the enemy. We will mobilize every aircraft possible, both training and "special attack" planes. We will smash one third of the enemy's war potential with this air force at sea. Another third will also be smashed at sea by our warships, human torpedoes and other special weapons. Furthermore, when the enemy actually lands, if we are ready to sacrifice a million men we will be able to inflict an equal number of casualties upon them. If the enemy loses a million men, then the public opinion in America will become inclined towards peace, and Japan will be able to gain peace with comparatively advantageous conditions.

https://irp.fas.org/eprint/arens/chap4.htm

>We have one example in the bombing but that doesn't mean that was the only option.

Yes, besides the atomic bombs there could have been an invasion or a blockade. Both of these options would have resulted in more deaths on both sides.