I think you're interpretation of the whole bdsm lifestyle is way of.
From what I've heard from both dom/mes and subs is that a sub will never be pushed beyond what he or she is comfortable with (discretion lies with the dom/me). Even if that boundry is pushed, it's done carefully and with purpose to reach a new level in satisfaction with sex or whatever else they are trying to achieve. A master's role is not to dish out any type punishment as he sees fit, even if a sub isn't protesting, it is your job to make sure she is alright.