It was well known even to the general public in the 1940s that the mechanism behind the nuclear bomb could generate vast amounts of cheap energy. It was known by nuclear scientists in the late 1930s that massive amounts of energy were released upon nuclear decay, and that chain reactions were possible, but that harvesting the energy for power generation would take some time.

I don’t believe there is anyone in the general public or who is an expert in any of the aforementioned fields (which have been around for 1-3 decades) that truly believes they are net positives.