I've been loathe to comment on this before because it is off topic (maybe the mods can move the Hiroshima stuff to a new thread), but I think I will now.
I agree with you - almost completely. I think that, as you say, the Hiroshima bomb was "the only option at that time".
The Hiroshima bomb was not the only option at the time. Two others that come to mind:
1. launch a full scale invasion of Japan.
2. Negotiate a peace
Option 1 would have been a bloodbath and perhaps unlikely to succeed: compare the D-Day landings and the enormous efforts required to make them successful. Then check the amount of ocean needed to be crossed to get from Britain to Northern France as opposed to from the USA to Japan.
Option 2 was politically unacceptable because of Pearl Harbour. I don't think Japan would have accepted any kind of peace that didn't allow them to keep some of the territories they captured. Japan was in a war with China and short of the resources needed to prosecute that war. That's why they launched the Pacific war in the first place.
It has been suggested that the Americans should have organised a demonstration of the atomic bomb on an uninhabited island rather than drop it on a major city, but the evidence suggests that Hiroshima had been selected as a suitable target some time before. It is enclosed by a ring of hills and the effects of blast and radiation would be contained. It was continually spared when other cities were subjected to fire bombing. Nagasaki was not a prime target and was only used because preferred targets were obscured by bad weather.
They only had two bombs. They probably wanted the highest possible impact to drive the message home to the Japanese. If they had just done a demonstration, Japan might have carried on "yes they've got this bomb, but they clearly won't use it against cities". One bomb wasted.
Another thing to bear in mind is that this really wasn't a huge moral leap. They firebombed Tokyo in March and caused comparable casualties and conventional bombing had levelled cities regularly in Japan and Germany with similar levels of casualties. Tokyo wasn't chosen as a target for the atom bomb mainly because there was practically nothing left of it.
Finally, imagine being president and not dropping the bomb and then invading Japan. What would you say to the mothers, wives and children of the million or so servicemen killed in the invasion of Japan in 1947 when they found out you had the means to end the war a year early?
