Thomas Midgley
Leaded petrol was the first, caused brain and nervous system damage leading to death of workers, and personality change to millions of babies and children especially, resulting in increased crime and violence in adulthood. Some rightwing people tried to blame liberal parenting for the rise in crime, and to credit zero tolerance policing for its decline, 20 years after the banning of leaded petrol stopped damaging babies brains, when those babies reached adulthood. The motor and oil industries and the politicians they paid, resisted the banning of leaded petrol for many years and are therefore responsible for the ruining of many lives, and untold crimes and murders.
Midgley cannot be blamed for his original invention, but he must certainly be blamed for suppressing and falsifying the evidence that would have shown its hideous results.
I think the second was fluorocarbons leading to climate change.