What does the practice of S/M do to our erotic reality? Eros gives our primal connection to all desire, all will, all choice. It is the root of finding our direction, of intuition, of the power to do. Sexuality, its bodily manifestation, is integral to its energy and inspiration, which we need in all spheres of our lives.
But S/M requires separating our sexuality from the rest of our lives, because we wouldn’t treat others that way in other contexts.
Borowing a term from Robin Ruth Linden, I’ll call this “alienation” of erotic desire.  Related effects I’ve read about also trouble me: habituation and desensitization.
An experiment at Stanford University in 1971 assigned twenty-four male volunteer students to the role of either “prisoner” or “guard,” in a simulated prison. All had been screened for psychological health. In the first five days, “guards” treated “prisoners” with increasingly harsh psychological torture.  “Prisoners” exhibited signs of severe stress. The experiment was planned for fourteen days, but it was terminated on the sixth, to prevent further harm.
Robin Ruth Linden comments:
Just as the “guards” made an easy accomodation to wielding power, we can expect that sadists who regularly practice dominant roles would become habituated to sadism, perhaps failing to comprehend its extremity.
I think Linden is using the term “habituation” to mean “the diminishing of a physiological or emotional response to a frequently repeated stimulus”: that is, the “guards” became less averse to cruelty the more they indulged in it.
Among the recent discoveries of neuroplasticity, the ability of the brain to rewire itself, a central principle says “neurons that fire together wire together.” With this in mind, psychiatrist Aaron Kheriaty warns that “BDSM causes the neural networks controlling sexual arousal, aggression, and fear to become dangerously intertwined.” Moreover,
with sexual behaviors, things get wired into our brain rather easily; even experimentation or dabbling has tangible physical effects. Undoing these new neural networks (or brain maps) is much more difficult and prolonged than the original process of forming them.
…Before making decisions about our sexual behaviors, we need to ask ourselves some questions about what we want to be doing to our brain and our body—what kind of neural tracks and networks do we want to be reinforcing through these behaviors? Do we want to be fusing sex and love? Sex and security? Sex and attachment or commitment? Sex and fidelity? Sex and trust? Sex and unselfishness? Or do we want to be fusing in our brain and in our experiences sex and violence? Sex and dominance? Sex and submission? Sex and control? We shape our brain by our choices. And we develop increasingly automatic and ingrained habits by our repeated choices. But the initial choice of which path we embark upon is up to us.
Argh. My concern exactly: if I indulge in masochism, it will wire together sexual arousal and the mindset of being a victim. But then my concern goes further: that masochism will spill over into nonsexual domains, encouraging me to be a victim in the rest of my life.
 Linden coined this term for me by saying ”I believe the recent interest by some women in sadomasochism is testimony to the profoundly alienated and objectified conceptions of erotic desire that our culture has produced. (Linden, ”Introduction,” in eds. Linden et al., 1982, 4.)
 Stanford professor Zimbardo, who ran the experiment, specified no physical punishment — but he also gave the “guards” explicit directions to create boredom, frustration, fear, and a sense of powerlessness. See Barker 2011. (For the article by Carlo Prescott mentioned there, see Valtin 2012.)
 Zimbardo, “Stanford Prison Experiment”.
 Linden et al. 1982, 9.
 Kheriaty, “Hooked Up and Tied Down” (Public Discourse 2/17/2015)