I've been thinking about this a lot lately. I do think there is a place for sadists (I mean, where else??) in BDSM as long as they keep control of themselves, as Emeyuchi says.

When my Master tells me he enjoys beating me he says it's because of where it takes me, that's the part that he enjoys, and he says if I were hating it entirely he wouldn't get anything out of it. He doesn't want to go to extremes, he wants to go just far enough. So he's not a sadist. We have been mulling this over.