Hersey's account of August 6, 1945 and the years that followed in no way gloss over the horror and terror of that day on the people of Hiroshima and Japan. This reflects his, and many others', view of the atomic bomb as a weapon that could destroy the world, as a weapon that is rightly feared.
That being said, Hersey does not sensationalize his account either. This is one reason why Hiroshima is a well-reviewed work, it successfully conveys that terrible day without appeals to emotion or fear. Hersey felt hopeful that mankind could avoid nuclear holocaust, and perhaps even move beyond having nuclear weapons someday. This attitude, reflected in his account, is important at the time because during the Cold War, many people believed nuclear war was inevitable. Hersey believed this was not so.