I think most of us feel pretty secure when the instructor or teacher knows more than the student, regardless of the field of study. But when it comes to putting the student at ease with a potentially deadly and dangerous and/or high risk activity like scuba, the instructors are essentially being paid to know more, instruct well, and evaluate the skills of the potential participants.
If instructors or teachers allow a person to "pass" or begin to participate in the field knowing that the student is a danger to themselves or others...
Scuba has long been a field where a participant needs to be a great judge of self ability, confidence, and safety. A diver must always be on the look out for food, drink, or activities that may influence their future dive, and that of their diving buddies. The ability of a diver to access information about themselves and others is always put to the test above and below the water. The ability level of others in the dive party is just as important. (The chain is only as strong as it's weakest link).
Self regulation is always the first line of defence. If your not comfortable with the instructor, the materials, or your diving group, you certainly don't want to put your life in their hands, do you? :wacko:
Any person that "teaches" a class should have a level of experience, knowledge, and ability that is an asset to the student. If regulation is required, so be it. But if scuba can continue to be a "passed down, self regulating" system, all that much better.