I wasn't trying to make a moral argument.

With the information available at the time, dropping the nukes was immoral, and unjustifiable. The public justifications and the ones accepted by the standard western historical narrative do not hold up to scrutiny.

Despite that, I'm claiming that the decision probably inadvertently saved lives.

But that's not a moral argument. There were other means to save lives from nuclear apocalypse, and the US is complicit in its own actions that they've done to ensure a cold war with the Soviet Union.