A friend from elementary school came to visit yesterday. She's kinky. (Roughly half of my friends are perverts. This is less because of some secret vibe we gave off before we even knew, and more because my friends are geeks and for some unclear reason liking Star Trek makes you like nipple clamps.) It's a little weird to discuss the finer points of caning with someone I used to play tetherball with, but I always like having kinky allies in the real world.
And we came to this rule, which I think might be a solid one: only do BDSM with people who are in the "scene." People who go at least sometimes to BDSM gatherings and events have an entirely different style than people who identify as kinky but have only expressed it in their own bedroom. Scene people are better at it, they're safer, and above all else they tend to be much much better at negotiating and respecting/expressing limits.
(This is not just a bottom problem; as a top, she's run into people who scared the heck out of her by being unable to express their own limits. "You were really hurting me back there and I didn't like it." "I wasn't hurting you in your vocal cords...")
Of course there are plenty of creeps in the scene and plenty of nice people who don't have the inclination to make their sexuality public. But niceness isn't entirely the point. It's more a matter of education and culture. Public BDSM communities have, when they're working properly, a culture based on explicit negotiation. Whereas most people's private sex lives are based more on nonverbal clues, guessing, and sometimes even pushing. That's okay (although not always) for just sex, but if you're going to be causing me pain and humiliation, wink-wink arm-around-the-shoulder ain't gonna cut it. We need to swallow our romantic spontaneity fantasies and talk.