What about the Vikings. or the Celts didn’t they wear fur?
The PETA message as I’ve interpreted it is that fur doesn’t make sense in sci-fi high-tech societies, so historicals and archaic fantasy settings don’t really factor in. The point, I presume, is to promote hopeful visions of a future where humanity has progressed past the animal-harvesting stage of civilisation.
In that sense, I could see the “wrongness” of, for instance, Captain Picard strutting around in an authentic mink coat. But a 40K Space Wolf wearing a fur cloak, not so much.