In general, when we talk about scientific discoveries we are inclined to see the good ones. Yet, how about the worst or most harmful ones?
For me, one of the most harmful and dangerous scientific discoveries of all time is the usage of uranium and plutonium as fuel in the nuclear power industry, creating tens of thousands of nuclear weapons that can destroy the world once and forever.
The very fact that these nuclear weapons are in the hands of a few "powerful" people it's terrifying.