I used to think I owned the right to my husband and several lovers before him. I don't think it's wrong to feel that way necessarily. Dangerous maybe, but not a bad thing... it made me realize how much I loved them and eventually made me realize that I don't own anyone except myself. It was part of a process that was necessary for my own freedom.
I was able to give myself over to that feeling, embrace it, forgive myself for it and then let it pass... it still comes up, but I see it in terms of wondering what I am missing that hasn't been looked at recently... mostly, have I had enough time with them... It wraps itself up in jealousy (or envy if I manage to still have compersion with the jealous feeling) rather than ownership for me now.
I don't think one is only poly in nature when one is able to give up their feelings of ownership and possession of their partner. I know some mono relationships that operate on the understanding that ones right to independence is important and necessary. It might not manifest in terms of taking on other lovers, but in other ways such as a hobby, going back to school, traveling... essentially poly could be looked at that way... a hobby
You are right, we are surrounded by messages that say we should be monogamous, but I don't see the message of "we should be co-dependent" as often at least. That I think is slowly changing the more people look at what keeps them from being happily in a relationship. One or more relationships.... maybe I am delusional or hang out with different people than you idealist?