He'll tear the moon from the sky and devour the gods. Now consider this story as an allegory. Fenris, I believe, is human instinct sometimes caring but often violent. What we call civilisation, learned behaviour and beliefs passed down, like genes, from parents to children. Like the cord it's manufactured from ingredients that can exist only as part of mental rather than physical reality, myths, beliefs and artificial emotions.
Humans are a domesticated species.
A domesticated species is a species whose behaviour has been modified through a combination of selective breeding and training to fit within the requirements of our society. A domestic animal is quite a different thing from a captive animal or even a tame animal. Fenris is not dead, merely bound. There's a permanent conflict between the bidding of our instincts and our society and, though most of us see it as necessary, we can't but resent it. This leads to perversion, which to me is performing an act because it's taboo as an act of defiance against God, Society or conscience.