It's an appeal to authority in an argument about authority. The question kubrick set up wasn't "is copyright law right" or "sensible" or "practicable"; it's "is it constitutional". The answer: yes.
So the law is within the bounds of common sense when it defines the copyright period as the life of the author plus 99 years? The constitution says a copyright is granted for a limited time to encourage artists to create. How is Walt Disney going to be encouraged to create another Mickey Mouse when he's been dead for 40 years?