That language behavior fundamentally misrepresents how a proper cons should actually work. It's a link between any two values, represented as essentially two joined pointers, one to each value. It represents a linked list when cons cells are nested, but that's just something that falls out of the far more beautiful and fundamental core axiom of the cons cell, not all of what cons cells are. Thus claiming cons cells must be nested (which is what requiring the second argument of cons to be a list (I.e. more nested cons cells or nil) implies) is actually bastardizing what a cons cell is, reducing it to a menial operation for producing lists that means the same thing as "prepend" instead of an elegant core abstraction you can derive further things from. Bastardizing it like this, honestly especially in a language for teaching CS, in the name of talking down to students, is unforgivable. I learned Common Lisp at 12 partially from Land of Lisp and partially from a Lisp 1.5 manual and experimentation. Properly learning the core abstractions was vital.