In the 1960’s, I had conversations with Nimrods who suggested that we should have dropped a “demonstration” bomb in order to reduce loss of life. That argument failed on two counts, both demonstrating their ignorance.
First, the U.S. was very early in their nuclear program and did not have the means to mass produce bombs. Nuclear bombs were a scarce commodity. Second, and most telling, was the rejoinder that if a demonstration would have been adequate, then why did the Japanese wait until after Nagasaki to surrender?
See my link at post #72, Bill Whittle addresses that in a cogent, rational deconstruction.