To answer this question, it is important to view this perspective as though you were an individual during this time. Perspective 2) "Harry Truman's decision to use atomic warfare against the Japanese during WWII was justified" is probably the most reasonable perspective for the following reasons:
1) American forces suffered heavy casualties on Iwo Jima (26,000 killed, wounded or missing in action) and Okinawa (46,000 killed, wounded, or missing in action).
2) During the planning phase for the invasion of Japan, it was estimated that the casualties could be as high as 1 million for the Americans. Japanese casualties were estimated to be even higher for both soldier and civilian.
3) Russia had a growing interest to enter the Pacific War to have a seat at the negotiation table to annex more post-war territory.
4) According to the Japanese warrior code, or Bushido, soldiers were encouraged to fight, and refuse to surrender.
5) American bombing, both conventional and firebombing, campaign seemed to have no effect in encouraging Japan's surrender.
6) It was believed that dropping the atomic bombs would, in the long run, end the war sooner and reduce overall casualties on both sides (Americans were unsure how long the war would last).
7) After dropping the initial bomb on Hiroshima, Americans demanded Japan's surrender, but was met with silence. Because of the silence, it was deemed necessary to drop the second bomb.
These are just a few reasons why this perspective is most reasonable.