Why were the following US military commanders against using atomic bombs on Japan?

One of the reasons could have been that they didn't want to live with the fact they dropped something so dangerous that killed innocent lives (those who had nothing to do with the Jap Army). Im sure it haunted them for the rest of their lives. I'm an American and I have lived in Hiroshima and I've been to the peace museum...What they used to have in the peace museum that portrayed the victims were horrifying and did not look human. Seriously, not something you'd want to live with for the rest of your life.