The destruction brought by the two nukes actually pales in comparison to the firebombing. Some have argued that, given the energies required to build the bombs, far more death would have occurred had those resources been put towards greater firebombing. In that context it is difficult to give special legal treatment to the nukes.
For true horror, continue the conventional bombing, and put an iron blockade around the Home Islands for another year and cut off all shipping. Millions would have starved.
US submarines were already very nearly doing to Japan what Germany's U-boats attempted to do to Britain by the late stages of the war.
Agreed. It is in victory where honor matters most. In naval circles there is a principal that a ship be sunk, not punished. (Shots not below the waterline meant to kill the crew rather than sink the ship and allow the crew to abandon.) Some say Bismark was punished. Walling off Japan and bombing it conventionally would have been punishment. Once the enemy is down, the victor has a duty to construct an endgame.
But imho the bombs are still overplayed as war-enders. I think the prospect of invasion and occupation by Russian forces had at least as much of an impact on the decision.