I spend a lot of time teaching students how to give good, constructive feedback as both uke and nage, so that the students can become their own best students. The teacher is simply a guide. Teaching students to become acutely aware of what is happening inside of their own bodies and being acutely aware of the connection with the partner is a very important feedback loop that is critical in helping the learning process to be more efficient, effective and within the realm of control of the student.
People may not want to hear certain feedback, but if something is not working and the same process is being repeated, bad habits are simply being reinforced that will later we harder to become undone. Everybody can offer some useful advise if they are taught how, when and what information can be of help.
Whilst I agree with the thread of your point Marc, there are times where the feedback that is given would entrench worse sins than being currently committed or is like introducing calculus to preschool children - they just will not get what is being said and will only become more confused. I think when discussing technique whilst training you should keep in mind a) the limitations of the recipient and b) your own limitations! I recall a post on another thread that was dealing with attitude / ability after grading that discussed just because you have proved that you can do a technique to required standard does not qualify you to correct others ad nauseum.
I am becoming a greater advocate for the "shut up and train" school of thought; like I said in my original post, but it still takes effort on my part but I will get there!!