Well said Joe. And as I understand it, you are in a closed relationship, so in practicality, you are monogamous — just with a woman who has another partner.
One of the aspects of a dominance hierarchy (like the one we live in)is that everything is zero sum. For someone to be up, someone else has to be one down; for something to be good, something else has to be bad. There is little room for nuance, cooperation, or a broad view. I see it all the time when talking about the particular experience of women. Some guy has to show up and say, “my problems are worse” as if one has to make a choice. “It’s not a contest” is a phrase I have typed a lot!
Talking about the benefits of poly lifestyle and the very real issues with monogamous marriage doesn’t mean that one is inherently better than the other. The humans involved are what makes that work — or not.