I have heard much condemnation in the past concerning S&M. Seems that there is much education lacking in the general population concerning S&M.
Let me give you an example.
She: Oh I'm not into pain, I could never do that.
He: Oh, well OK. Let me as you then, do you like a little spanking during love making?
She: Yes, I do, it heights my senses.
OK, in a small way that makes my point. It is all about limits. Since it is all about limits; it has to be about negotiation. "I like this, but I don't like that." Secondly it is about trust. One "usually" doesn't just "jump" into bed with another person. There is something that says, "yes, I can do this with this person." That's trust.
How far one goes in receiving painful stimuli is in direct proportion to the ensuing pleasure that it gives. Endorphines turn the pain to pleasure.
S&M is not for everyone for sure. But it shouldn't get the bad rap of being a perversion. It is just another way of doing things.