I think everybody agrees that immutable data-structures are preferable to mutable ones if it is possible to get by without mutation in practice. In Haskell it s

I think everybody agrees that immutable data-structures are preferable to mutable ones if it is possible to get by without mutation in practice. In Haskell it seems it is difficult to mutate data, whereas in Lisp not so. If immutability is good then it would seem it is best if you can enforce immutability at the language level. I'm just wondering whether mutability is a downside of Common Lisp?