It makes more sense that we have to fight humans, because the Unitologists have basically been going around the galaxy and systematically eliminating all of the Earth Gov Forces and anyone who opposes their mission plans.

Jacob Carver, and Edward Norton and their crew are the only ones from Earth Gov which survived. That's it.

Makes sense Humans would be something we would be fighting against.

And those Brother Moons are disturbing AF. They are lovecraftian horror that telepathically screw with you with hallucinations, and horrifying visions and speak to you as a means to mess with you even more. All they want is food and are parasites.