Re: abusive sensei
I think a lot depends on whether the teacher's goals are aligned with the student's goals. I'll forgive my teacher a lot if he's trying to make me a better swordsman; much less if he's trying to show what a great swordsman he is.
I'll also forgive my teacher for being human. If he thwacks me occasionally in the process of teaching me to move, or not to be open, because I'm not as fast as he thinks I can be or simply because he miscalculates, that's just part of the deal.
But all that should be the exception. If he's misjudging by a lot, one would have to wonder why.