AshaShanti,
I was weirded out when a friend described to me her forays into this sort of play. But from the way she described it, it wasn't about cruelty or pain but mainly about being close to another person in a very.. er.. intimate way. I don't pretend to understand it well, I'd just say each person gets something different from that sort of play, and it's not all monstrous or evil. Actually, it's not a far step from vampire rp, when you think about it. SL's been dripping with vampires for years.
Anyway, it's not my cup of tea either but I wouldn't get too worried about it.