Originally Posted by SchrodingersCat
I'm a firm believer in the notion that the only people who get a vote in how a relationship works are the people in that relationship.
Yes. Some people want nothing more than to be the boy/girlfriend-on-the-side. I should hope that's not what poly is all about, but I think we can agree that such an arrangement does fall within the definition of poly, so long as each participant understands and agrees to the arrangement for what it is.
One consideration that was largely missing from this thread is that of children. Poly is whatever you agree to, but parenthood is its own sort of commitment, with its own category of moral and ethical issues worthy of debate. Many parents will choose to maintain a structured household that prioritizes a stable family environment, such that polyamorous connections must be hierarchically subordinated ("secondary") and subject to extra restrictions. When kids are involved, it would seem to me haphazard to operate with the only rule being "don't be an asshole."