That. That hug in page 13, and the "thank you".
This is what people don't understand. Not like I'm an expert either, but anyway.
S&M is not for everyone; true. You don't like it? Fine. But don't push your views on them.
She WANTS pain. She ASKS for it. And he gives it to her. And when they're done playing, she lets him know that it's fine. He did exactly what she wanted.
That's the cornerstone of this type of relationship: trusting your partner.