OK..so obviously my opinion is skewed but....I find myself asking this question a lot lately. Not for myself but for people who are in a primary relationship i.e. husband and wife. The back and forth happiness and sadness, peak high and peak low don't seem worth it to me but I am not poly. There rarely seems to be sustained balance or stability but perhaps this is because a lot of my exposure is with people that are struggling and the really happy established poly relationships are not apparent or visible because they are simply living it. Even with Redpepper and Polynerdist I don't get it....I still can't quite figure out why it is worth it to them and if they wanted to become "not poly" I would totally understand. I think a part of me would even be very happy because I understand the feeling monogamy gave me and associate it with calm fulfillment. Again, this is because I am monogamous and can't truly appreciate poly for what it gives them.
I'm hopeless I know