He's right. Many people find it easy to understand erotic role-play or even gentle bondage, but when you start talking about intense sensation play (a.k.a. pain)... well, then they start to get nervous.
First, let's address the "why would anyone want to" issue. Intense sensation can function as a symbol. Some people want to feel "not in control," and they don't need a lot to get there; a collar and leash, a light spanking, a little role-play, and boom, they're where they want to be.
Some people need more than that. Intense physical sensation can pull you out of your head and into your body in an undeniable way. No matter how strong--or strong-willed--you are, your flesh is powerless against an 18-gauge needle or a buckshot-weighted singletail. The sensation takes these people down--and, remember, that's what they want. It's still about relinquishment of control, it's just that some people need a more vivid demonstration of it than others.
Psychology aside, people are all wired differently when it comes to intense sensation. When I negotiate scenes with people, sometimes they say, "Well, I'm not into heavy pain." I have to tell them that there is no carved-in-stone scale of what defines heavy versus light pain. What is painful to one person may barely register with another. Part of what affects how someone perceives intense sensation is their body's endorphins. Endorphins are neurotransmitters, chemicals that are directly involved in the brain's electrochemical workings, and they're your natural painkillers. Intense stimulation, especially if it's carefully sustained at just the right level, will result in an endorphin high. (It doesn't only happen in SM; long-distance runners, for example, refer to it as a runner's high.) Some people get very tranquil and blissed-out, others get loopy and giggly. But for me, the draw of heavy sensation play can't be reduced to mere chemistry. It's more like alchemy. And the beauty and the power of watching someone take pain and magically transform it into pleasure is something I never get tired of seeing.
