The way I see it is that polyamory is a new perspective on relationships. It focuses less on the idea that your partner is your possession and more on the idea that your partner is with you because they want to be with you. It deals with jealousy in a way that treats it as a sympton of a deeper feeling than the problem itself. It focuses much more on honesty and communication.
So I think this can work for multiple partners or just one.
I really only have a problem for judgemental monogamists who see my idea of a relationship as sinfull, morally wrong and broken without even listening to the idea with an open mind.