Of course, the A-bomb disasters could have been prevented! The U.S. government could have refused to order and pay for the development of the bomb. Those who made it could have refused to make it. Those who tested it could have refused. Those who loaded it on two planes could have refused to load it. Those who flew the planes and pushed the buttons over Hiroshima and Nagasaki could have refused. The American people, if they had known enough, could have refused to use it as a weapon of mass destruction -- the worst of its kind so far.
Yet people today still seem unwilling to take responsibility for stopping war and weapons development. There is lots of evidence that war no longer works as an effective instrument of foreign policy. But until masses of people revolt against war, and until economic systems stop depending upon the arms industry, there is not much hope of change for the better.