We have (for now) restrained ourselves from the more vicious applications of technology to war, in the form of nuclear, biological, and chemical weapons. Although I could see the argument being made that such has not occurred for strictly humanitarian reasons, but instead as a predictable consequence of game theory.

In less important matters, we've regulated many harmful substances that the free market would love to poison the populace with. Nicotine, trans fats, gambling, alcohol. Some regulatory interventions have been more successful than others...