I think it's the latter. It's tough to take this song seriously. A line like "whips and chains excite me," is just plain silly. These words don't describe a relationship, just a masturbatory fantasy. The accompanying S & M video is truly awful. (It's so bad, I refuse to supply a link to it). The production is amateur, with gratuitous strobe effects, and psychedelic camera angles. Even worse, you've got a grinning Perez Hilton on a leash, lifting his leg at a fire hydrant. The rest of this repetitious mess is a collection of cliche fetish images. Rihanna's posing and gyration does not reflect anything substantial about sadomasochism or BDSM.
And it's too bad. Rihanna's Rude Boy lyrics, for example, are actually far more evocative of kink reality:
I like the way you touch me there.I believe the song S & M is intended to court controversy in order to sell songs. There's no social awareness program going on.
I like the way you pull my hair.
Happily, there is a development in the popularization of BDSM that is significant. Colter's Daughter, an erotic romance by Maya Banks, is on the NYT e-book bestseller list. This novel has D/s themes. Yay on Maya!