Evidence

It was justified to drop the atomic bombs because the japanese attacked us and got us pretty good so to prevent further attacks we had to take control and to do that  kill the japanese.
The United States in the latter days of WW2 was faced with a terrible dilemma. The Japanese are a proud, courageous and determined people. Japanese men, women and children were willing to die for the emperor. The invasion of Japan was necessary to end the war, because the Japanese would "lose face" if they considered surrender.
The United States had to choose between sending hundreds of thousands of US soldiers, many freshly off the battlefields of Europe, to invade Japan killing and being killed by the hundreds of thousands, or dropping a newly developed weapon called the atomic bomb on two cities in Japan which would result in tens of thousands of civilian lives with little loss of US servicemen but the only way to end the war quickly  and honorably was to drop the bombs.

Reasons for Revenge
 On December 7, 1041 at 7:02 A.M. army radar at Opana tracked down a cloud of aircraft flying overhead from the north. a Fort Shafter officer concluded it was a flight of B-17s on their way in from California. At 7:49 A.M. a wave of 183 Japanese airplanes start an attack. 40 torpedo bombers and 49 high-altitude bombers attack battleships other planes attack airfields. Then at 8:55 A.M. the second wave of 167 planes replenishes the attack on airfields and ships.  
        The United States was under attack with no sort of warning and no reason for attack. Japan showed that they were prepared for war and wanted to attack while the U.S. was weak and unprepared. The United States had already lost a ton of me in Pearl Harbor to the Japanese and shouldn't lose more to the Japanese when they are willing to die instead of lose in battle.
(Casualty chart of Pearl Harbor and everything destroyed in the attack)


                             (Shows that at least 50% of people will have an instant not painful death)