Logically, any sort of lust towards something that isn't a human being you actually have met is self-destructive and degenerate. This also applies to porn stars and having celebrity crushes. You are going after a person you have never met before, will never meet, likely has a relationship of their own, and will undoubtably reject you if you were to ever meet them.
Of course, this doesn't stop people from having waifus, crushes, and fetishes towards things they will never get. Furfags are just a subcategory to this degeneracy.
