It's probably fair to assume that Truman had more immediate and frequent casualty reports and projections than Oppenheimer. So the former was weighing against

It's probably fair to assume that Truman had more immediate and frequent casualty reports and projections than Oppenheimer. So the former was weighing against alternatives, and the latter was weighing against inaction. In Oppenheimer's defense though, at the time he couldn't have known that (a) the US would refrain from using nuclear weapons in subsequent wars, (b) other countries would rapidly acquire nuclear weapons, (c) MAD would become normalized as the only acceptable use of nuclear arms. None of which were guaranteed to pass, meaning a very different perspective in 1945.