Difficult question to answer, but maybe there is an expectation of a certain mental toughness that is expected of students. I notice that the degree of "abuse" escalates as student progress through the ranks. I have also noticed that abuse is use to weed out certain students at lower ranks. Upon receiving my Sho Dan it was clear that the gloves were off and anything goes, a significant but progressive change from brown belt. Whether this has benefit for developing mental strength is up for debate. But lets face it, a real fight situation, whether you see it coming or not, requires a certain mental fortitude. Most real fights are won or lost on mental strength, so perhaps there is a real place in training.

As I have watch various Sensei(s) (plural) it seems to me they use abuse as a teaching tool as much as get out of my house tool. In the later case it is used against student who refuse to listen and/or take on the responsibilities of their rank in respectful way. In the former it is used to help get over the mental hurdles in actual being aggressive. Not everyone is really prepared to be aggressive. And I recognize this as the Sensei push different students according to their limits bring them along at a sustainable pace, helping them to develop controlled aggression.

Of course there are abusive people in all arenas and that skilled fighter abuse others is not shocking, even up to and including 8th degrees. I suspect when a student confronts such a situation there are no easy answers.

Abuse is as much about perception as it is about intentions and pain.

Something to consider...