Having read a fair bit on the subject, (mostly by way of exhausting youtube's supply of documentaries about that era) I've actually concluded that not only that horrible event was inevitable at the time due to how Japanese leaders were being rather "difficult" - It was perhaps some strange kindness (though a particularly unpleasant one) to have done
anything to force the war to an end at that particular time.
The alternative scenario would have been unimaginably more horrifying, yes, more so than a pair of nukes (which weren't really even as destructive as other bombing missions done with less novel ordinance (such as the far deadlier fire bombings))
What Japan had in store should the war have extended into late 1945, was not only a US invasion in a mind-boggling scale (which was predicted to cost about a million allied casualties) - But on the other side of the islands, there was the even more trouser-soiling presence of a Russian army still larger than that, and with a previously unfinished bone to pick with the Japanese.
Had the war not stopped exactly right there and then as it did, it's pretty much safe to say that afterwards, there would not be a country left to call Japan.
This scenario would totally suck for several reasons, as the Japanese have proven quite excellent friends and makers of outstanding videogames and great food in the decades since.
Imagine a world without Mario, or Sushi... That might have been our lot, should the war have been allowed to continue the way it was headed.
It might also be argued that perhaps as the not-so-reasonable species we are, Humans were bound to have nuked themselves at some point in their history.
Having done it in that particular point in time, might have been the lesser of whatever unknowable evils could have been, if instead some other less self-critical culture happened to be the one pushing the button in anger for the first time...
Also, it's worth noting how ever since war got so absurdly nasty that even the winners weren't too happy about what they did to get there, if one would add all the casualties of every war that took place ever since that day, it wouldn't match even a fraction of the dread statistics of 1944 alone.
So despite what history-ignorant people tend to say about "the world getting more dangerous every day", the numbers prove quite the opposite. This less-than-peaceful planet of ours has actually never been as safe.
This video puts it all in quite eye-opening perspective:
https://vimeo.com/128373915
Makes one think, people who say those things never considered what it'd be like to have Genghis Khan for a neighbor :uhh:
note: my exact figures and numbers might be some ways off (as I write this off the top of my head) - so don't quote me on that. The general point still stands, though.