Ah. Well, I do think that it's in poor taste for D&D to malign a relatively reasonable kink like that. I mean, they don't use Catfolk or Dragonborn to bash on furries or Changelings to bash on transformation fetishists, so why should S&M be singled out like that?
This also reminds me of the Yuan-Ti from my setting {:coughshamelessplugcough:}, who routinely mutilate themselves to practice their own brand of blood magic and whose god is a giant skinless snake with nails pounded into his muscles and hung up by hooks on the celing, dripping luminescent blood...
And they just so happen to be the good guys, using said blood magic to keep the Tarrascon (Essentially the Ur-Tarrasque, the being upon which all Tarrasques across the multiverse unconsciously base themselves and who could make Tharazidun pee his pants in fear) sealed within the setting and being willing to teach their magic to those hardy enough to withstand it and unselfish enough to use it for others sake and not their own.