I, personally, NEVER found that grades devalued my learning. They NEVER prevented me from learning or from enjoying what I was learning. I enjoyed getting good grades. I saw them as a validation of my hard work. When I did not get a good grade, I focused on what I missed and learned from my mistakes. I even went to my teachers / professors to get help when needed.
Here is my response:
It's important that to note that you said the word "I" eight times. While you may have a very good idea about your own opinion of grades, are you sure you are in touch with how most people feel about grades. Also note that you placed an exorbitant amount of faith in the grades you received. The assumption is that high grades mean a good thing and low grades a bad thing - the point is that you did then (and I fear still do) believe that grades are reliable, accurate and objective. How often did you get a good grade and go the teacher/professor (or think to yourself), "hmm, I wonder if this is really indicative of my learning. I wonder what mistakes I could learn from despite my high marks."
Remember the real reason we assess children is so one day they can grow up and assess themselves. Grades all too often rob children of an opportunity to become autonomous learners who can properly self-assess without being told how to do so.