One of the acronyms you need to know if you think of engaging in BDSM in real life. Safe, Sane, Consensual.
As for how it relates to game play, the way I see it, if it isn't safe and sane, the domme isn't really in control (maybe no one is, but I'm less about the sub's lack of control and more about the domme's control). And if either side isn't consenting, then it's not a relationship with an aspect of power exchange, but rather an event of rape*, which, again, isn't something that I fantasize about.
*CNC, or consensual non-consent, where the submissive agrees (consents) in advance to situations where their consent is not requested, enabling rape or kidnapping scenarios, is a different issue. I'm referring there to actual lack of consent.