You're absolutely right- at the end of the day it's a job and with whatever you bring yourself to sell, even if it's quirkyfying symbolic visuals to make someone look better, customers need to take into account that designers operate by understanding and reforming malleable reinforced concepts which is not something you can learn overnight. Although practice makes things easier for a designer, there still is nevertheless a lot of invested time on behalf of designers, time that cultivates skills which creates products of function, thus a service which shouldn't be free at all.
Just how gutted would you feel if someone made an absolute fortune from a design you did that heralded nothing for you at all.....?
Believe me, it has happened more than once, it is one reason behind my cynicism.