There was an interesting piece in Observer magazine about a murder with what is called in article 'S&M' connection:
http://www.guardian.co.uk/theobserver/2008/apr/13/1

There is clear implication that the masochist was an unlikely one because he was squeamish and that it was about self hatred.

Without Stuart or Charlotte's knowledge, Rod had for some time been advertising on an S&M website that he was looking to be someone's 'slave'. If they had known what he was doing, they would both have been surprised. Rod had been mildly curious about S&M when he was with Stuart - nothing more than what Stuart called 'schoolboy stuff' - but Stuart wasn't interested and Rod hadn't pressed it. Not even after they split up did Stuart ever see marks or bruises on Rod's body.

Rod was an unlikely devotee of S&M. He was squeamish. The sight of blood made him queasy. He couldn't even look at a broken fingernail, and Stuart was later convinced that Rod's attraction towards masochism was rooted in self-hatred. He was sure that Rod saw his separation from Stuart as a deep rejection. Rod had been abandoned and he was lonely and now he was punishing himself. The self-hatred, thought Stuart, was all mixed up with Rod's upbringing, in particular his relationship with his father. He had constantly sought approbation from his father, but he felt that he never received it.

It is possible he did hate himself, but from my reading, he was more like a sexualised kid in a sweetie shop who'd been interested in BDSM, but not had desire filled before. His interest in young men and BDSM may have been self-loathing, pleasurable fun or anything between if not a mix of both ends of the spectrum.
Whatever the trigger, he had a curiosity and interest. And people into BDSM are as mixed a bag as any. While not squeamish, I am a bit of a coward about pain avoiding dentists and injections where possible. I suspect I'm not alone in having masochistic/submissive fantasies and desires but being wary of pain. My fear of pain was a barrier to exploration (among other barriers!)but fascination and curiosity got the better of me and reality is rather wonderful.
Sadly for Rod Hall, he became the victim of a most violent and horrific murder. he absolutely did not deserve to die, but he took enormous risks with somebody who showed signs of being seriously unsafe. It is very sad, but is not typical of those who choose to explore BDSM fantasies.