Sample scenario for all on either side of this "narc-out" discussion.
You are a friend of a student pilot.
You notice many problems with the content of lessons being given to your friend. You inquire further and find out that there are significant gaps in knowledge of the individual and determine that the instructor has not given your friend the required information at all. No familiarity with flight following, not much radio communication knowledge, doesn't know what a steep turn is, was free to fly solo to any airport he wanted to, made frequent flights to his beach house which is a long cross country flight, had no sign-offs for anything, etc...
You know the instructor and have flown with him as an acquaintance many times. On several occasions, this instructor has done things that were very unsafe, and certainly, illegal. Flying inside the pattern of another aircraft at an untowered field because the other aircraft was taking too long and had too wide a pattern. Covering the windscreen to practice IFR scan.
Your friend calls you up and says he is quitting because the instructor made him fly toward a thunderstorm, albeit a light one, because "you'll need to know how to deal with turbulence sooner or later." They also almost ran out of fuel on the way home and had to divert because of it.
He contacts the FSDO to complain about the instructor and the FSDO contacts you regarding the instructor.
How do you proceed?
I don't believe that ratting out the pilot, just because he is flying again is right, personally. Unless you know he is doing it illegally. Then, yes. But, if the FAA grants him another chance, then they feel that he has learned from his past mistakes and has moved on. From the sounds of it, though, the pilot in the original post is not likely to continue unless he gets a special issuance, considering his condition.