How can I despeciesize the word "dehumanize"?
Of the many words with relevant overtones (such as abuse, mistreat, degrade, downgrade etc), I can only suggest one serious candidate that is not species-specific and avoids too much notion of abuse while representing an attitude of mind rather than physical behaviour:
Objectify = to treat as an object (the complete quotation says: “or cause to have objective reality”, which is not relevant in this context)
Merriam Webster