A part of the Christian imperialist worldview, the idea that 'Man is above animal and they were created by God to be used as Man sees fit', has been the cause of endless horrors. Without this human-supremacist view they would treat other people better too, even if their enemies were 'subhuman', if they had compassion for animals.
It makes me think of the connection between 'masculinity' and eating meat in the West. It's seen as effeminate to eat vegetables or be vegan, this idea helps reinforce a worldview centered on violence and exploitation.