In my uninformed, pacifist opinion, we could have allowed the Japanese to surrender conditionally. It's always seemed to me like a fight where one guy has the other guy pinned on the ground, but breaks his arm because he won't say uncle.
I could be wrong about that though, so whatever.
I believe that there are, essentially, only two reasonable and defensible arguments against the atomic bombings, given the historical record.
The first is, as I said, if you broaden the argument to say that strategic bombing generally is immoral and/or unnecessary. In which case, of course, the argument isn't really about the atomic bombs any more.
The second is to take the position that the Allied demand for unconditional surrender (with the caveat of the Emperor's survival) was itself unreasonable.
I, however, would still argue strongly that unconditional surrender was a rational, reasonable, and necessary demand.
You have to consider the context. In 1945, the world had been driven to not one, but two devastating global conflicts in the span of thirty years. The Allies were not
*just* fighting the Second World War. They were also fighting to make sure that they wouldn't fight the Third World War thirty years down the road.
What is the alternative to unconditional surrender? That, after invading Okinawa, the United States simply "walks away", saying "good game guys, you fought hard, but so long."? Completely unnacceptable. That would leave in place the Japanese militaristic regime, that completely dominated the existing political system, and would risk Japan rebuilding with the same sense of
revanchism that Germany developed between the wars, and thirty years later you would still have a Japanese regime that was militaristic and expansionist.
No, the demand for unconditional surrender was a rational policy and, as horrific as they were, it was the atomic bombs that shocked the Japanese leadership into accepting it and allowing for a smooth transition.
edit: Or, to continue with your awkward analogy, you didn't break his arm *just* because he wouldn't say uncle, but because he was still struggling, and had every intention of standing up and slugging you from behind if you just got up and walked away. Or of nursing his wounds and going back to beating up the smaller kids in his neighbourhood after you walked away.