This is the part of your post that was mainly my bone of contention and your statement that history supports this. We will never know if America would have gone to war even if we were not attack, but IMHO I think its unlikely, at the very least it would certainly not have been immediately, evidence seems to support this.I think the US public was fully prepared to go to war with japan over tha Japanese attacks on British and Dutch possessions in the Far East. The Japanese certainly believed this to be the case, and so rejected a "non-American" solution to their problems. They knew that they would never ave as good a crack at US forces as they would have on December 7th, and so their plans always included an attack on the US.
Elliot Morrison; the widely respected official USN Historian, writes in "The Rising Sun in the Pacific"; "Supposing Japan attacked British, Dutch or French possessions, would the United States consider it a casus belli? Even President Roosevelt knew no answer to that question, and Captain Purnell could only guess. Mr Roosevelt by that time believed that the US should oppose, with force, if neccessary, any japanese advance into Malaya. But he could not be certain of obtaining a declaration of war from Congress on that issue, which would certainly have been interpreted as "sending American boys to support tottering colonial empires"
Morrison goes on to write in his epic "Two Ocean War"
(quote); There was no threat, express of implied, that the President would ask for a declaration of war on Japan if Tojo rejected it. The cold war could have gone indefinitely, so far as Washington was concerned (and we now know how long a cold war can go on), provided Japan made no fresh aggressive move. And its is doubtful wherther Congress would have considered as casus bellia Japanese move into Thailand, British Malaya or the Netherlands East Indies.
In his book "Roosevelt and Churchill" Joseph P.Lash cites on p.225;pg2;
Adm.J.I Richardson CinC US Fleet in his testimony before the Joint Committee on the Investigation of the Pearl Harbor Attack,(quote) Adm.Richardson also quoted Roosevelt as saying in reply to his query of whether the US was going to enter the war that, "if the Japanese attacked Thailand, Kra Peninsula(Malaya),or the Dutch East Indies, we would not enter the war, that if they even attacked the Philipines , he doughted whether we would enter the war, but that they(Japan)could not always avoid making mistakes and that as the war continued and the area of operations expanded sooner or later they would make a mistake and we would enter the war".
Regarding US populus will to fight. Morison further states in "Rising Sun in the Pacific"p.18;pg1 That a Gallop Poll taken after the "Panay insident" showed that 70% favored the complete withdrawl of the Asiatic Fleet,Marines,Missions and Medical Missions from China.
Morrison cites on P.39,pg4; another poll taken prior to Pearl Harbor, which ask the question "How far should the US go?" 6% said fight, and 82% favored an embargo.
All this seems to imply that most of the US populus plus much of the Congress were unwilling to go to war to save european colonies. Even if FDR and many in the military deemed it neccessary.