I agree to never [there's that word again] argue with your teacher, but do give him feed back that is constructive. So when s/he instructs "Never use false fingerings", say, "Dr. Onady says you are setting yourself up for defeat wiht that comment"... OK scratch that last comment. But inquire, "Can you play a shake for me on the high C." OK now, could you try that shake with just the 2nd valve. What do you think is it easier or harder with the 2nd valve? Do you feel the intonation suffers in easing the shake by using this substitute fingering" OR ASK: "In the double high range when tone pitch is so close, would single valve substitutions for double valve notes bring these notes more into pitch. Could you demonstrate this for me." In this way, you are not arguing, your are requesting feedback. I call this "reframing the question". Stating "Dr. Onady says you are setting yourself up for defeat with that comment", I call inflamming the question which IS worse than arguing.