Wow, I did a double take, you sound like me. When I said something similar praising Haskell's effortless parallelism, someone made a reply that lead to my learning Clojure.
Racket /also/ has `thread` which is a co-routine but afaik you cannot pass the co-routine off to another native thread and there are certain constraints passing data between different threads, similar to transferring ownership.
I am not aware of the SBCL ecosystem to comment.