Laurie…
Again - I think GM is a brillant horseman and his willingness to share his knowledge and to pass down as much of his wisdom as possible are to be admired and should be examples to other senior statesmen in this sport. The fact that he does this for no compensation makes it all the more impressive.
It is interesting that you mention his threatrical background - that, and his age, go a long way toward explaining some of the behavior that has been noted here.
I have no doubt that many of the students in these clinics need discipline and strong words to correct problems. They should be tough enough to take criticism - and even strong criticism. I would have no patience with them if they were not prepared to do so.
That being said, my most recent comment was not so much directed at GM (although I am of the opinion that personal insults are not appropriate and not the best method of education) as to the culture that seems to think it is perfectly OK to insult the person rather than the error.