Grading on a curve
Correct me if I'm mistaken, but if you grade on a curve, the grade becomes an indicator of how well you did relative to your fellow students. It turns the class or the test or whatever the case may be into a contest between students.
If you don't grade on a curve, the grade is an indicator of how well you learned the material. It's entirely independent of how well or how poorly others may have done.
So what's the goal of education? To do better than the kid you sit next to, or to learn?