I agree with you, and felt similar seeing posts like that. I am new to the community so I didn't feel I should speak on it, but I consider it more of an aspect of my identity than a "choice" or "relationship dynamic". I do not believe that I could be in a monogamous relationship without suppressing part of myself. I believe that is similar to how a gay/lesbian person could "choose" to be in a heterosexual relationship or a straight person could choose to be in a homosexual relationship, but they would be suppressing who they are and would not be fulfilled by it. I am not saying it is the exact same, and I would assume it is to a lesser degree. However, the language surrounding polyamory as a lifestyle choice is incredibly reminiscent of the puritanical language surrounding homosexuality as a sinful life style choice. While obviously the people practicing polyamory are not referring to themselves as sinful, it still mirrors the "its not who you are, its a lifestyle choice and you can choose to stop being that way". I do not understand the assertion that it can't be an identity because it is a relationship dynamic. homosexual and heterosexual are also words that describe a relationship dynamic, and they are also identities. Actually polyamory means "many loves" and does not describe a relationship the same way "monogamy", which means "one marriage" does. That's semantics, but still.
I understand that many people disconnect it from their identity and only see it as a relationship dynamic, and I respect that, but I don't respect the assertion that other people, who do not share that belief and instead they do see it as part of their identity, are incorrect.