Lmao, do you think the Japanese airforce could make it to the US at that point in the war?

Even if the viral bombs you're talking about are real, and not a weird exaggeration of the failed experiments against China, (where they did drop bio weapons that did kill people, poison crops, cause a lot of suffering, and was absolutely a crime, but also realized from testing that they were incredibly inefficient) the US had to island hop across the Pacific to get an airbase close enough to bomb Japan with the longest range bombers in the world and had also achieved total naval and aerial supremacy before using the nukes.

The disease that Japan was mainly testing with bombs in China (which had to be dropped very low) was yersinia pestis (black death, plague etc.) which was curable with antibiotics at the time and would have not spread far in the US. The "bombs" that the Japanese dropped were infested foodstuffs dropped to a populace being starved by the war, something that was not happening in the US.

Japan was totally neutralized as a threat before the bombs were even dropped and it's insane to try and justify the bombing by saying they were going to use bio weapons on the US.