S&M question.... Sex or ABH, GBH, & Self Harm?

People within our society have been sent to prison for taking part in S&M because it causes actual or grevious bodily harm.... so why are the ones that like to be punished, not treated as self harm patients? If you were an alien from another planet, visiting earth to research self harming in humans, what... show more People within our society have been sent to prison for taking part in S&M because it causes actual or grevious bodily harm.... so why are the ones that like to be punished, not treated as self harm patients?

If you were an alien from another planet, visiting earth to research self harming in humans, what would you write in your research book about the topic of S & M?
Update: I know lots of people enjoy a little slap and tickle... but for the purpose of the question, I'm talking about the really heavy stuff, obviously.
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