Regarding the whole "Is it racist to assume they would commit suicide..."
Prior to the planned invasion of Japan, the US forces invaded three islands with significant Japanese populations: Saipan, Tinian, Okinawa. (Iwo Jima, the other island they invaded that had been Japanese pre-war, was evacuated of civilians beforehand).
An estimate for the population of Tinian (least defended) pre-war would be along the lines of 20 000. 4000 civilian casualties are recorded, including many suicides.
For Saipan, estimates seem to be around 25 000, perhaps 30 000 civilians. Estimated civilian casualties range around 20 000, including 1000 civilian suicides on the final day of the campaign alone - the total number being much higher.
For Okinawa, estimates look at about 300 000 pre-war population. The estimate death tolls range rom low 30 000 to well past 100 000 (the USMC and the Okinawa prefecture both estimate past 100 000). Again, a significant portion of that was mass suicides.
Beyond the mass suicide, there was the tendency of the Japanese army to hide snipers and ambush parties among civilian buildings, and even more so to hide them in the exact same kind of caves (turned into death traps for Americans) that civilians also tended to seek refuge in. When you always have to be mindful of being shot at, it's rather difficult to tell the difference between the people hiding in a cave that are civilians and the people hiding in a cave waiting to come out at night and kill you and your friends.
In any event, apply THAT kind of civilian casualties to Japan itself, and the one million estimate starts to sound less orientalist racism, more painful optimism.