But as Kevin Leavitt pointed out the acceptance of corporal punishment in the Korean culture. One could speculate that this does apply to most Asian cultures as well. Malice or not, it is accepted and practiced.
Intent to train or intent to harm...where to draw the line. Perhaps the intent to harm comes from not only a cathartic need on the trainer's part to vent frustation or sadism but as Gurney Halleck said to Paul Muad'dib Atriedes in the original Dune;
Paul: "Gurney, I'm not in the mood to train right now."
Gurney: "Mood...MOOD? Mood is for loveplay and cattle...now guard yourself for TRUE!!!".
Paul's beloved Master-At-Arms attacks him with a feigned fury in order to make Paul react. Now if a sensei/sempai were to do that to judge your response and see where your basics need help in, would it be justified?