“It is my opinion that the use of this barbarous weapon at Hiroshima and Nagasaki was of no material assistance in our war against Japan. The Japanese were already defeated and ready to surrender because of the effective sea blockade and the successful bombing with conventional weapons . . . My own feeling was that being the first to use [the atomic bomb], we adopted an ethical standard common to the barbarians of the Dark Ages. I was not taught to make wars in that fashion, and that wars cannot be won by destroying women and children.

give me a 1 sentence main idea

The main idea of this statement is that the use of atomic bombs in Hiroshima and Nagasaki was unnecessary and morally wrong, as Japan was already on the verge of surrender.