He labored out this strategy both at the degree of a social system as a complete and at the stage of assorted social subsystems, such as state, financial system, science, faith, schooling, artwork, family, and—the concern of the current article—regulation.
The necessary issues conceptual naturalism supposedly permits us to do (e.g., morally consider the legislation and determine our ethical obligations with respect to the law) are literally rendered more difficult by its collapse of the distinction between morality and law.
I’m not certain the answer to the puzzle (“why does Simpson think any of this states a dispute with Hart’s theory of legislation?”), however it probably has one thing to do with Simpson’s (bewildering) view that Hart’s thought of a rule of recognition specifying the last word standards of validity in a legal system evinces “absent-minded conformity to the concept that all legal guidelines originate in legislation”.
This enables Kelsen to take care of the same understanding of the nature of normativity as Natural Legislation’s conception, particularly, normativity qua causes for motion, without having to conflate the normativity of morality with that of regulation. As an empirical matter, many pure legislation ethical theorists are also pure law legal theorists, but the two theories, strictly talking, are logically independent.