The student is trusting your evaluation of thier performance and assuming that you have made an informed accessment of their abilities. After all, that is your job. IF you make a poor accessment and then the student crashes while landing that is the instructors fault alone.
I figure there are at most three guys in my club (not including me) who have never crashed on landing or takeoff, maybe not even that many. Are you saying that the rest of the members should never have been allowed to solo, because their abilities had not developed to the point at which they could always land or take off without making a mistake? If that were how we did things, RC flying would be a very small hobby.
Your approach would seem to make instructors responsible for all crashes anyone has had, even after they have gone off on their own. After all, if we had made an informed "accessment" of their abilities, we wouldn't have said they could solo.