What is the opposite of anthropomorphism?

The opposite of anthropomorphism is dehumanisation. It is the process whereby people fail to attribute human-like characteristics to other humans and treat them like nonhuman animals or objects.

Dehumanisation involves describing members of a particular outgroup as less sentient and civilised than the members of an ingroup, and thus not worthy of humane treatment. A typical strategy is referring to the targets of prejudice as “vermin” or “animals”.