I've never accepted that.
I did say it was arguable. But I'm convinced, as were Truman and his generals, that a ground invasion of Japan, which was the planned alternative to the A-bombs, would have caused at least as many Japanese casualties as the Hiroshima and Nagasaki attacks, and more importantly from an American point of view, a tremendous loss of American lives. I, and many others, applaud Truman for making his decision on that basis.