Johann Hari offers some good sense:
Sadomasochists are as sane as the rest of us. The psychologist Stephenson Connoley found they were no more likely to be depressed or insane than you or me. It doesn’t appeal to me, but it seems to be a way some people leech out their anger or lack of control. Fine. Let them.
There is an easy solution. In Britain, you are currently allowed to consent to injury in four specific situations: sport, surgery, piercing, and circus performing. Why not add sadomasochistic sex?