I don't care what stories you may have heard out of someone's mouth, or what tales you've been reading online, no Dom or Dominatrix--no Master or Mistress--gets away with total, absolute cruelty towards a submissive.
Real submissives know this and by real submissives I'm referring to the ones that actually, physically participate in BDSM play not the ones who simply fantasize/talk/write about it. I'm referring to the ones who do it. The legit ones, not the talkers. The ones who know what it feels like to be in leather or rubber or lycra bondage gear, the ones who've been brave enough to surrender to another man or woman taking on the role of Dominant. The ones who've been bent over a spanking bench (or a bed, that works just fine), the ones who can truly recollect the different sensations involved in being bound to a St. Andrews Cross (for example). The real submissives, not the fantasizers.
Real submissives know that there are lines and there must be a degree of mutual respect between themselves and the Dom. Yes, even in hardcore humiliation/degradation/pain play. There must be lines. There must be an aspect of consideration in play even if it's silent while the scene is in full swing. But the understanding, and the care, must be there.
There are some people who mistakenly believe in the myth, and the value, of the relentless, vicious, out-of-control BDSM Dominant. Don't bother.
Sociopaths aren't interesting. They're a dime a dozen. They're missing pieces from their puzzles. They're stereotypes. Cliches. The world has a ton of them.
BDSM "Sadists"--the ones in the BDSM context--, the ones who do belong in dungeons, the ones who should be tying people up and "abusing" them (willingly on both sides, needless to say.....), are those who have a sense of understanding. They know what's real and what's not real. They know what's called for and they're familiar with that very specific, delicate boundary between what's right and what's wrong, what's fantasy and where those fantasies end.
The real Masters and Mistresses are the ones who are able to maintain some kind of a balance between "cruelty" and care/consideration.
If a prospective Master or Mistress doesn't have a grasp on that concept, if they don't get it, if that idea seems just too compromised--too unidealized--then they won't have submissives. Not, at least, for any substantial amount of time.
All Masters and Mistresses have to be careful, considerate people (even when they're pretending that they're not). Of course. That's rational. That's reasonable.
The unstoppably mean, vile S&M Masters and Mistresses don't have submissives for a substantial amount of time. Not in real life. That's a fact.
Either find a realistic balance on how to treat people (or, preferably, have an understanding of that balance innately inside of you) or don't do BDSM. It's very simple.