Thank you very much for starting this OP. It's very interesting and I think it's becoming a much more acceptable and popular way to live. My DH and I are discussing it, primarily because we're both just a bit bored.
Although life-long monogamy works for some, it really is miserable for others.
The posters who have had very angry and emotional responses should perhaps interrogate those feelings. Why do you feel so threatened by people choosing to live differently? So what if some people want to 'have their cake and eat it'? Is that a crime - if everyone is a fully-functioning adult who knows the score and has agreed to the T&Cs in advance?
Bear in mind the marriage vows we use today - till death do us apart etc - were written in 1543 when most people lived till about 30 and most marriages lasted a decade. Humans beings are not naturally monogamous despite the state trying to convince us that we are.
The type of open marriage that appeals to many isn't even about wanting to shag about with reckless abandon, which seems to horrify so many people.
Though I absolutely accept that life-long monogamy works for some, why is it so difficult for some people to accept that it simply doesn't work for others? There is no right and wrong here. There is life-long monogamy - which has become, in our culture, the societal norm, not because it's 'right'. But there are other ways to live happily ever after.
This article talks about it very eloquently. www.theguardian.com/lifeandstyle/2017/jul/23/polyamory-new-way-to-love-men-women-sex-relationships-elf-lyons
Thanks again OP.