Now there are as lisais mine said people who will go above and beyond what is required of them.
To me that is just plain stupidity, if you want to do something that is sure to do you unwanted harm, emotionally or physically then I would have to ask why are you an idiot?
I have done questionable things, have attempted questionable things, but I always know the risks, and I am fully prepared to deal with the consequences. I won't go beyond what I know I can't do.
I sometimes cannot understand how others would enjoy certain types of play, but I at least try.
It all comes down to each his own really, and as long as that is what YOU and the other person wants, as long as YOU know the implications of that type of play, and as long as YOU are completely fine with it, then I don't see it as being abuse.
We all do things that at times may damage something, be it scars on skin, becoming ill, or emotionally breaking, but that is up to the individual to take care of themselves and to know and be prepared for the risks involved.
What's fine for me may not be for you, and vice versa, but I won't lecture you on how it's gross, evil, nasty or wrong.