Dehumanization comes naturally. In children we hear it when one child says to another, "you're nothing but (fill in the blank)."
Adults are much more crafty, so they turn to systematized ideologies such as 'evolutionary scientific materialism."
Evolution says all things, including human life, emerged out of a void or Big Bang from which came matter.
Put together, evolutionary materialism says humans are nothing more than aggregates of matter in process of evolution or perhaps hominids evolved from apes.
There it is: the way to dehumanize humans who must be gotten rid of. Just inculcate this dehumanizing ideology into the minds of people in the name of science and they will accept the necessity of antihuman depopulation agendas disguised as sustainability, necessary to save the planet, and so on.
Thanks