What were the alternatives? A negotiated settlement with Japan? I guess a few (one?) of the more naive Japanese strategists entertained that fantasy, but that was never considered by the American side for a nanosecond. An invasion on the Japanese mainland would have killed hundreds of thousands of American military and, almost certainly, many more Japanese than were killed at Hiroshima and Nagasaki. Truman was right.
IIRC, Tojo was hatching a plan to kill Hirohito and blame it on the Americans, which most likely would have kept the war going.