Wesley J. Smith has a piece at First Things that should send chills down the spines of every reader. He argues that the radical environmentalist movement represents an "ongoing convergence of deep misanthropy, radical Malthusianism, and renewed advocacy for wealth redistribution." In other words, a profound contempt for humanity conflated with a fear of dire ecological consequences from overpopulation and a yearning for economic egalitarianism is hurtling us into frightening times.
Radical environmentalists (as opposed to conservationists) see human beings as a blight, a "plague upon the earth" to use David Attenborough's phrase. For many of them we're a toxic bacillus whose numbers need to be severely reduced.
The suggested means for the needed purgation are all, we're assured, non-coercive, but if our presence on the planet is such a cancerous curse why would Darwinian materialists, if given the power, not favor whatever means are necessary to bring about ends they deem so overridingly urgent?
What sort of means might we be hearing about in the not-too-distant future? Forced sterilization, compulsory abortion, elimination of the aged, infirm, and criminal, etc., are no doubt some examples, and why not? Why, given a materialist, naturalistic worldview, would any of these be wrong? Why would it be wrong to kill people if such measures are necessary to save the planet? As atheist superhero Richard Dawkins put it, "What's to prevent us from saying that Hitler was right?"
All that stands in the way, in a secular society unmoored from the belief of earlier generations that every person is created in the image of God and is precious to God, is the task of acquiring sufficient media and political influence to legislate those kinds of policies into law. A culture which no longer values life will have no difficulty finding ways to promote death.