Can you be so sure?
What are you really measuring come exam time? It's not an objective measure, that much is sure. Someone who is loaded with work, family, and various other considerations isn't given a due handicap, and even in the event that there is a curve in place, it's still not measuring much. We'd do better to recognize that the measure of man is almost always going to result in spurious data. A D student isn't necessarily dumb, but disinterested, or distracted, perhaps disenfranchised or something along those lines. And grading itself really isn't revelatory, it's easy to game. I just did it, open book quiz with a digital copy, I ctrl-F'd through it and found the answers with ease, I didn't read much of anything, but I did get a perfect score. What does it say, then? That a student can exploit Campbell's law, and the teacher can do the same, so the district can look good and continue receiving grants. It has nothing to do with intelligence, it has to do with sculpting the metrics to say that someone is intelligent. Grading wasn't always the case, mind you, it was an invention of the late 1700's - and frankly a bad one. But institutional inertia carried it to the present.
What I assure you won't result from dismantling the systematic psuedo-objective measurement of humans is "cognitively handicapped" generations.