I think that the pathologizing (I know, that's not really a word...) of sexuality is a huge problem. It's done all the time with regard to BDSM; I've heard many, many people make the assertion that BDSM practices are not "wrong" in an ethical sense, but are instead "unhealthy" or the manifestation of something "unhealthy." I'm not into BDSM personally, but I find it greatly problematic to divide sexual behaviors between "healthy" and "unhealthy." For one thing, it seems to be a mere cop-out to avoid condemning someone outright ("I'm not saying their behavior is wrong or immoral, I'm saying it's unhealthy and they need help," which is just as patronizing and stigmatizing as outright condemnation would be). And of course, it creates the same distinctions between what people should and should not be doing. I think a lot of people think of non-monogamy in that way: we're all acting on some "issues" that we have. The non-monogamy itself may not be a pathology, but it's seen as a symptom of some underlying problem. There must be something wrong with us if we don't fit the traditional model. Homosexuality isn't in the DSM now, but it was until what, the 70s? Which just goes to show that our concept of "healthy" and "unhealthy" sexuality is not a fixed thing. I think the other problem with this division between what's healthy and what isn't is that it automatically normalizes everything on the "healthy" side of the line. If you're someone who's not into being tied up, that's fine. But if you're not into, say, vaginal intercourse, then you're a weirdo for *not* being comfortable with something that is "healthy and normal."
Sexual behaviors, relationship structures, gender identification, etc. shouldn't be divided between notions of "normal" and "abnormal," in my opinion, but as individual desires/preferences/inclinations that are all equally valid. Treating everything as though it's some kind of illness (look at Tiger Woods and his "sex addiction", for example) seems to be the trend these days for continuing to condemn others, but doing it in a more PC way.