Not all military leaders felt that dropping the atomic bomb was ethical. One example is Admiral William Leahy, he claimed that the Japanese were going to surrender and that they were already defeated because the Americans had already invaded some surrounding islands of Japan. Here is a quote from him
"The Japanese were already defeated and ready to surrender because of the effective sea blockade and the successful bombing with conventional weapons."
Another example is General Dwight Eisenhower. He thought it was unnecessary.
A quote from General Dwight Eisenhower:
"I voiced ... my grave misgivings, first on the basis of my belief that Japan was already defeated and that dropping the bomb was completely unnecessary, and secondly because I thought that our country should avoid shocking world opinion."