Ah, Claire, I love your analytic mind. It's got a very Virgo, detail-oriented quality. Maybe rising or moon or mercury?
Anyway, yes, excellent points all. My sig other has much experience in Dialectical Behavioral Therapy and has helped me understand the difference between observing/describing on the one hand and forming a judgment on the other. My own mind tends to jump right over observing/describing and forms judgments as if they are observable facts. Returning to the simple moment of just letting things unfold and observing and describing them has helped me reduce the oppressive weight of my own judging discriminator.
It does seem that non-monogamy and polyamory are subject to some labels that then require a bit of sorting out. It has been important and difficult for me, for example, to reach the determination that I am *both* non-monogamous and a sex addict. It looks to me like lots of people who "cheat" on their monogamous partners can now take refuge in the label "sex addict," and not do the sometimes more difficult sorting out of perhaps being highly sexually and relationally unconventional.
Simply put, non-monogamy is an illness in the eyes of many, a character defect. Similarly for some, monogamy is an illness, a character defect. You are right, of course, to point out that this need not be an issue for anyone.