My father was on a yard mine sweeper (YMS 389) and would have been in that first wave trying to sweep mines in Tokyo harbor. Do you think he ever regretted them being nuked? Neither do I.
The math is easy and horrific. Take the Japanese, American and civilian deaths on Okinawa and extrapolate those to the Home Islands population and armies that would have been engaged. It added up to death on a horrific scale on both sides. Still, no surrender.
The ONLY thing that got the Japanese to surrender were the bombs. And even at that the Army darn near rebelled.