What does the author mean by saying that dropping a nuclear bomb strikes at the very basis of moral existence?

A nuclear bomb is far more destructive than any previous type of weapon, and it can be used to kill thousands, hundreds of thousands, or even millions of people all at once, depending upon the size of the bomb and the location where it is dropped (the bombs dropped on Hiroshima and Nagasaki killed hundreds of thousands of people). The moral basis of existence would seem to be a respect for our fellow human beings and for their lives. To kill people in such wholesale quantities, and so indiscriminately, shows a lack of respect for human life. Normally, we try to be very careful about killing people. Even in times of war, we normally try to kill only enemy soldiers or enemy insurgents, and not to kill civilians who are not involved in the fighting. A nuclear bomb just kills everyone in a given area, including babies, and others who have no involvement in whatever conflict has motivated the bombing. Human life becomes very cheap in such circumstances. Life become irrelevant, meaningless. People are of no more importance than ants, and can be snuffed out as easily, when you are dealing with nuclear war. This would appear to be an immoral attitude. One can also argue that there are some circumstances which would justify the use of nucear weapons - a good case can be made for the use of atomic bombs in WW II. Nonetheless, there are serious moral issues involved in killing so many people, by means of a weapon of mass destruction.