To some extent I agree - deliberately harming someone is not on. However in this situation the arm was dead only for a minute or so after - no torn ligaments, no permanent damage - It was a shihan letting an overly compliant uke know that a) he could tell where the limits of uke's flexibility was, and b) don't lead the ukemi. Oh, and uke WAS (and still is) a doctor...
If my teacher chose to not respect my tap and release his hold on my command, it would be the last time I train with that teacher (If I didn't get up and lay a beating on him).
Respecting the tap is the single most important thing that can happen on the mat. It's not my training partner or my teacher who has to live with the injuries. They do not know better than I on what my body can or can't take. Unless they are willing to go to my job for me and pay my mortgage they have no say in this matter.
In my opinion, not respecting the tap is the single most irresponsible and disrespectful thing someone can do on the mat.