There's a paragraph in what is an otherwise mostly remedial article on the subject that I think bears inspection, as it's a sentiment that needs to be repeated more often,
Sadism isn’t the only paraphilic category for which the question of harm can get murky for psychiatrists as well as for anyone who has ever contemplated another person’s unusual sex life. As the lovely Kate Upton reminded us earlier, a universally objective reality simply doesn’t exist in the present domain; what’s harmful to me isn’t necessarily harmful to you, and vice versa. It will change as soon as I put this comma right here, but as of this very moment there are exactly 7,088,343,858 people on the planet. If all but one of these individuals were to experience harm in exactly the same way from a certain sex act, that solitary person is nevertheless just as right (or just as wrong) as all the others combined. This is because there’s no “correct” way to experience a sex act, only individual differences in subjective realities. It may be a moot point, since it’s not logic that guides culture but instead sheer social mass shouldering into it with brute force, but nonetheless 7,088,343,857 shared subjective realities do not add up to a single objective fact. What was harmful to them was not harmful to him, and that, as they say, is that. Or to rephrase: one person’s horror story is another’s erotica. And I’m quite sure our vorarephile Bernd Jürgen Brandes would tell you so too, if only he were still around.