I don't see any defensiveness, I see people attempting to answer your question. You're not into it, which is fair enough, but it is very, very hard to explain to someone who has no interest in it. I wouldn't have understood it myself if not for my experiences. It seemed abnormal and dangerous to me as well. (Which is why I spent so many years repressing it.)
I already said that I don't enjoy pain to the extent that OP does. I have had sessions that lasted for hours though, including the odd break. I'd be surprised if OP and her partner went at it for four hours with absolutely no rest or respite, but again, that's for OP to answer. As is any question about whether or not she's been abused.
I was/am unusual in that I never did participate in sessions with people that I wasn't in a relationship with. I need a certain connection and dynamic with my partner for it to work for me, and I very rarely met the right person. That's just me. My partners were never into blood though. Light bruising, perhaps, but I don't mind that myself either.
I COULD wax very lyrical about what my submissive life does for me, the dynamics and so on, but I don't think OP's thread is the place for it. Perhaps I'll start an AMA myself, although I probably won't.
The comparison to harvesting organs or any other form of abuse based around commodifying and selling one's body, presumably based on desperate poverty rather than sexual desire and satisfaction, is offensively stupid.
In my experience, any Dom whose actions were not based on consensual and satisfying, mutual pleasure got very short shrift within the community. Others' experiences may differ; perhaps it's regional. I find that abusive men tend to find victims pretty easily and don't need fetish clubs. I've seen far more to worry me within my circle of new/newish mum friends.