I agree in full. I would like to point out your example of the nuclear attacks on Japan. Just as importantly as it saving all of those lives, the nuclear bomb was looked at as just a BIG bomb. After we went in and discovered the massive genetic problems associated with nuclear exposure, it became much more known just how damaging these things are long-term.
We cannot take nuclear weapons back. That genie is already out of the bottle. One thing that we can do is build defense systems to take out missiles that can deliver them.