I thought the article was very interesting and it made sense to me. Of course there is as much potential for abuse and coercion in the BDSM scene as there is within "normal" relationships/sexual encounters. You get abusers in all walks of life - it makes sense that they would exist here too.
The main problem seems to be - as seen here! - that most people seem to think that if you engage in BDSM (as a submissive) then you "probably wanted it anyway", and what did you expect? ie, denying that any abuse can ever take place within BDSM. Which, if you think about it, is as ludicrous as saying that there is no such thing as rape within a marriage. Just because someone is "submissive" that doesn't mean they consent to everything at all times. It is my understanding that the intention of the "contract" is to outline the boundaries and make them clear before the "scene" starts, so that the sub doesn't have to come out of character halfway through and say, actually, I really don't want you do to THAT. From the article, it would seem that in practice it's quite common for contracts to be broken, which to me shows that they're not working in the intended manner. Also, it sounded (again going from the article as I don't have personal experience of the "scene") as though once one is in the moment, as it were, it's very difficult to protest anything - I'd imagine that's a heavy psychological effect rather than anything physical although of course it might be difficult to protest if you've been bound and gagged, or something.
Of course there's the view as well that all BDSM is abusive and I can see the point of that, but I wonder if it's a bit simplistic.