The left believes that the world has several billion too many people. The left gets what it wants, and it wants massive population reduction. A recent novel by Dan Brown is attempting to make the idea of mass, involuntary sterilization respectable, or - at the very least - to “start the conversation.” It may be five years down the road or it may be thirty years. Just gassing people would be too obvious, so it will be done through mass sterilization or some sort of “accidental” catastrophe. Perhaps global warming will be the scapegoat for the outbreak of some mass epidemic that is actually human-caused and deliberate.
For what it’s worth, mass sterilization is preferable to mass starvation.