The 'No's that have posted have all made very good points; I think it's just a question of some variation in the interpretation of 'necessary'. My interpretation is as I described it in my first post, plus the fact that I personally believe (I stress that - this is only my own personal belief here) that once one achieves a certain level of experience in a particular field, it becomes a moral responsibility to pass that knowledge on to a new generation of practicioners. Case in point from my own history: A young soldier joins the Army, stumbles his way through Basic Training, Battleschool and Regimental training. He is taught by his superiors - Master Corporals and Sergeants who pass on to him their knowledge in bits and pieces. Along the way, he becomes experienced; serves overseas, gains rank. He has become the type of veteran he once learned from. It now becomes part of his responsibility - heck, his right
, to take newcomers under his wing, to train them. To do otherwise - to hold himself aloof from young soldiers - would be shirking his moral duty to pass his knowledge on. Teaching is another rite of passage and more; until he chooses to take it on, he will not advance much farther, since he won't accept the responsibility required to advance.
I personally believe it's the same in Aikido, or Karate, or acting, cooking, science or any other field you wish to name.
Anyway, that's my response, in my own interpretation of the question.
I am admittedly and unashamedly biased on the matter, teaching's 'my thang', as they say.
P.S. - Kent; in your quote (thanks for responding, BTW), you put in the line 'thought experiment snipped'.
No probs with snipping it, of course, no need to repeat it, but I must emphasize it's not a thought experiment - it's a very real and valuable training technique used to show new teacher just how valuable their job is. Like I said; try it; you'll be amazed how well it works.