Despite what's shown in 50 Shades, the BDSM community is big on things like safety, awareness, and knowing what you're getting into. I'm unsure if BDSM desires come from something out of the ordinary in the way someone is wired, but I don't consider it a "mental disease" because of that. Successful, functional people do partake in it plus a lot of other unexpected sexual pastimes, even if it seems like the whole world is having vanilla sex outside of a few unfortunate perverts on the news who've injured themselves trying to get their jollies.

Childhood trauma can impact pretty much every aspect of your life. Not everyone into BDSM has a traumatized childhood, though, so it's not like they have to accompany each other.