As I understand, modern research has disproved the Freudian-ish claims that people that are into S+M are likely to have been abused and experienced psychological trauma while growing up.
What it comes down to is some people like to be dominated and some people like to be subdued. Some like a level of both. Do we really know why some things are sexually stimulating? I'm into feet, for crying out loud.
Instead of turning to others for enlightenment, try making your own observations and coming to your own conclusions. Not only that, but try opening up to it. Try spanking the guy you've been talking to (very, very hard) and you may find seeing this guy go into a fit of euphoria after very stimulating yourself. In my experience, if you show a guy that they can be open about the things they like in bed without fear of judgement, they'll love you forever... well maybe not forever but you get the idea.
I was once seeing a guy that loved his nipples bitten and pinched to the extreme. At first I thought it was a little weird, but when I opened up and went along with his fetish... I've never heard someone scream out and erupt so volcanically until then.