I won't pretend to know what was in the minds of the people at the time. Maybe there were multiple reasons and not one single "real reason."

Looking at the world today I think most people would prefer that a device that can cause such massive destruction simply not exist. I can only imagine what will happen once the ones that have been 'lost' start showing up in the wrong hands. The destruction was bad enough when in the 'right hands' (scare quotes, because I don't feel so great about what we(USA) did either.)

We can play what-if all day but we will never know what would have happened if things didn't happen as they did. I just hope that the actual version of what happened doesn't get 'corrected' in history books so that our future descendants can learn from our mistakes.