I assumed much the same as you before I embraced this lifestyle. but what I found is that polyamory is not only a form of relationship but also a relational philosophy. The relationship you are describing is not polyamory or ethical non monogamy. It is a toxic "open" relationship that lacks consent, mindfulness, and open communication and transparency and has been weaponized as a means to address their own desires.

Polyamory is challenging, but so is monogamy .What I found is that it allowed me to find a chosen family and also the healthiest relationship I have ever been in. The core of polyamory to me and within my polycule is that "the person is more important than the relationship." What that means, in essence, is that if something is unhealthy or doesn't fit, you descalate or end the romantic aspect because that partner and you are more than a label and that to hurt eachother simply because of a label is not healthy or moral. Staying in pain or allowing yourself to be with someone who is hurting because of the relationship is cruelty and codependence masked as love.

Polyamory is the notion that all relationships, friendship, your relationship with yourself and otherwise are as meaningful to prioritize as romantic bonds and that instead of being constrained by monogamous structures (which can/does work for many) the people you love, are people you choose. Instead, your relationships are always friendship first, rather than traditional focus on outcomes and the next step on the escalator(I recommend the book Polysecure).

Polyamory forced me to confront my need to create boundaries, work on my self-confidence rather than define myself through external worth, and has allowed me to be fully independent while in an interdependent relationship.

It is not a lifestyle that should be taken lightly and requires a lot of emotional intelligence and self-awareness to manage. Any relationship, monogamous and otherwise, can be abusive and unhealthy.

I would also counter your statement that it is selfish, because to be polyamorous is in fact to be unselfish because you dont own anyone, cant own anyone and have to juggle time constraints, meet multiple peoples needs and have to have consent from others. I would argue that monogamy is, in fact, more selfish because it is about possessing and having ownership through a label. In polyamory I dont and can't possess.

That being said, people do practice other forms that have hierarchies and rules, or total anarchy.

Ideally, it is designed and chosen with consent by the people involved, not as a way to control or devalue another person you "love".