My comment regarding competition finishes was made so that a pointless death like that of Neil Lawson could be prevented without detracting from the sport. Safe flying is all about risk management but a total prohibition on certain manoeuvres and aspects of gliding will do nothing to improve overall safety.
The link above mentions that Mr Lawson narrowly avoided being hit doing something similar the day before he was killed. Some people (and I would include the OP in this judging by the tone of the question) just won't get it until something drastic occurs ie the instructor walking off. If the instructor had not walked off, would the OP have come on here and asked? Probably not. If the instructor had carried on with the lesson it is far more likely the OP would have ignored anything said (actions speak louder than words after all) and carried on with their reckless stupidity. The instructor was instructing by not instructing.