You’re assuming “it’s a violation of trust!” is the hazard in this situation but that’s a very shallow, naive understanding of why having two “partners” is almost universally frowned upon. See the sibling comment for a full write-up.
The human psychological and interpersonal aspect is the real hazard. You either A) don’t find two other people that can emotionally handle it or B) do find two other people that can emotionally handle it but suffer from the trauma they’ve experienced that numbed them enough to be able to emotionally handle it, which is a hazard in itself. Either way, it just doesn’t work in the long run.
Respectfully, this is a deeply misinformed perspective. I am not some naive dreamer, this is a journey I have been on for nearly 20 years. Over ten years ago I decided I needed to learn how to do non-monogamy properly, and in this time I have read plenty of books on polyamory, monogamous relationships, and personal growth. For over a decade I have had the guidance of a supportive therapist who has studied non-monogamy professionally and works with multiple non-monogamous clients. Some notable books on polyamory I have read are "The Ethical Slut", "More Than Two", and "Polysecure".
I have practiced non-monogamy for 9 years, and along the way I dated a lot of people who were only doing it because they wanted to date me, and I was non-monogamous. Those situations always go poorly. Now I only date people who both want to be non-monogamous for their own reasons and have read the books and done the work to learn how to do it properly.
You are incorrect in your suggestion that people who learn how to do poly well do it by becoming numb. In the terms of the book Polysecure, people learn how to do non-monogamy properly by learning ways of fostering secure attachment that don't rely on monogamous concepts. That book explores the existing body of research on secure attachment, which is primarily focused on monogamous relationships, and applies those concepts to polyamory, with the ultimate takeaway being the HEARTS method described here: https://www.kcresolve.com/blog/creating-a-secure-attachment-...
You are incorrect in your two options presented, which both boil down to "you cannot find emotionally healthy polyamorous people". In my community in Oakland CA, with the people I tend to date, polyamory is actually the norm. You can find people who are immature and problematic, and you can find people who are stable, emotionally mature, and willing to do work when needed to maintain healthy relationships. I have learned to broadly differentiate between the two types pretty quickly. Note that I am 39 and tend not to date anyone younger than 35.
I currently have two partners. They are both dating another person who I will call M. I am also friends with M, and M and I actually text more than I do with either of our mutual partners. We've been having movie nights recently that are cute and wholesome as hell. I've never seen a whisp of jealousy or related issues amongst us. We've all been poly in this community for long enough, and we are all in therapy, that we have learned how to navigate things.
I hate to say it, but "poly simply doesn't work" is what every person who has lived in a monogamous culture and hasn't done the research is likely to say. It's absolutely not easy to learn how to do it and is very much is not for everyone. Some people really should just be monogamous, that much I have learned. But to make the blanket statement that it doesn't work in the long run is sorely misinformed, and if you gave that advice to someone who trusted you, who actually did need to do the work and learn how to be polyamorous, you could do serious harm to their life. If I had tried to stick with monogamy, it simply would have been wrong for me and would have led t continued misery.
It took a while to get here, and I know all too well the pitfalls, but I have finally learned enough, and critically moved to the right place, and now I am flush with lovely non-monogamous connections that fill my heart with joy. I have two loving partners and I go on lots of dates with other cute people. My relationships are healthier than they have ever been, and I finally feel like I have found myself.
So please, don't go telling people that non-monogamy doesn't work. It isn't easy to learn how to do it, and it is not for everyone, but once you learn how it actually becomes second nature (if its right for you) and can be really easy. Non-monogamy saved my life, and there is a wealth of research available exploring how it works. Even if you don't want to be poly, its well worth learning about.
The human psychological and interpersonal aspect is the real hazard. You either A) don’t find two other people that can emotionally handle it or B) do find two other people that can emotionally handle it but suffer from the trauma they’ve experienced that numbed them enough to be able to emotionally handle it, which is a hazard in itself. Either way, it just doesn’t work in the long run.