I've seen a lot of conspiracy theories but nuke denialism is a new one. Do you think the US is faking it and the rest of the nuclear nations developed nukes, or the US was faking it but no longer is, or everyone is in on the conspiracy?

The answer to 1 is the always-popular "dilution is the solution to pollution", although that's not good enough for all cases, see the concept of "low-background steel".

I also don't think fire bombing and carpet bombing could explain the very nuke-specific effects observed in Japan. Remember, not everyone in the targeted cities and surrounding areas died, and to the survivors, a carpet/fire bombing is quite obviously different from a nuke. Faking it with 10000 tons of TNT (or "perhaps a larger amount") is kind of hard (unless you want to claim that the Japanese were in on it) when the largest heavy-lift aircraft (An-225) had a max takeoff weight (not payload) of 630 tons and was built decades later.