I have never experienced behavior from a coach or sensei that approaches the level of abusiveness described in this article, but I have tolerated (or even been amused by) behavior by both that I would not tolerate in any other context. I don't feel bad about doing so, and I don't think that the coaches/senseis in question were in the wrong; I also got right up in the face of a PE teacher in high school once when I thought that he was being abusive towards other students, so I don't think that I've just been a pushover.
I've also been offended by behavior in both coaches and senseis that no one would say even strays from
workplace behavior norms, based on the underlying attitude that I felt was displayed.
http://www.salon.com/2013/04/05/why_...usive_coaches/
Another area where coaches are, shall we say, 'less than respectful' is in physical therapy. PTs can cross the line of outright cruelty at times, pushing patients until they're crying or screaming at them... and be thanked by the latter for it later.
For me, I think that the answer to the 'why' of the the article's title revolves around trust: even with behavior that is superficially outside of social norms, I have never tolerated anything that I did not feel, based on a long-standing relationship, was ultimately in my best interests. Honestly, I wouldn't want to train in a context where a coach or sensei felt like they couldn't occasionally break social boundaries in order to make important points.