A prime example is Lothrop Stoddard who incited murderous hatred under the color of science, specifically anthropology and eugenics.
Most of these deaths have been textbook eugenics based on the idea that some people just shouldn't be allowed to live.
But a great many of these deaths (at least 50 million) are a direct result of "environmentalism" which resulted when Rachel Carson wrote "Silent Spring" and "scientists" decided that it was okay to let tens of millions of Africans die of malaria to save birds (even though a link between the dead birds and DDT has never been established).