I see what you are saying in reply to Ice however, I too have seen where the poly person makes decisions for the mono person. Not just in teh example of, "I've fallen in love with someone else and figured out it's okay for me to love more than one person so we are a poly marriage now, you can accept or walk." Which is still totally inappropriate.
There have been examples right here on this site of the poly person saying that they and their new partner have decided together that they are SOUL MATES and so the mono spouse is just the 'comfy' relationship. Where the poly person and their new love have decided that they can be sexual but they want to be sexually monogamous so the married or established mono partner is suddenly told no sex for you with your partner! There are many more inappropriate examples when you put D/s into it and I have seen myself on here where the poly person has met a mono person, 'converted' them, and then the mono (their new playmate/partner) has told their established partner that things have changed. No discussion, no lead in, just that because their new poly partner says this is the way it is, they are doing it that way.
I'm not vilifying D/s, or poly, but I also see more often than not the will to vilify monos and 'mono thinking' and labeling them 'mononormative' like it's a bad thing. Yet when a poly makes a mistake or is inappropriate the automatic distancing done with comments like, "Oh well they are bad polys!" or "That's not the right way to do poly so we aren't talking about that!"
If you can put all mono in a box and whether someone is doing it wrong, right, or is scared out of their mind and has no idea what to do, then you can do the same for poly. So while it's wrong for a mono partner to decide what is going to happen in a relationship not their own, it's wrong for a poly too. No disclaimers, no buts, and no distancing yourself because it makes you feel bad. I feel bad every day for stupid shit women pull, I feel bad that it gives women a bad name. I feel bad every day for stupid shit poly people pull, feeling it gives poly people a bad name. I don't try and distance myself I simply explain to myself and to others that EVERYONE does things wrong at one time or another. Some learn from it, others not so much. I don't care if they are men, women, mono, or poly. If it's inappropriate in a relationship, it is inappropriate. I'm not going to make excuses for those that fit my 'label' just so I can put all the inappropriate, or the vast majority, on someone else's 'label'.
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year