As far as sex and relationships go the thing i myself personally cackle at is the whole open and polygamous "relationship" tosh (basically the ones where they also claim they are in a "proper" long term relationship)... cut for length
I think the term you mean is polyamorous since polygamy isn't legal in most places. I think people's views on this will depend on whether they believe that people are naturally meant to be monogamous or that monoagamy is a social construction. And also, in some cases, whether you see sex and love as two seperate things.
It doesn't surprise me to hear yet another person coming out with the cliche that if you're in an open relationship one or both of you can't be satisfying the other partner sexually, but I am surprised to hear it coming from someone I took to be openminded and someone I didn't think would make such lazy assumptions.
I personally don't believe that its natural for humans to be monogamous, I just think its the preference that the majority of people seem to have (although whether that's down to actual preference or taught behaviour I don't know). I don't see choosing to have a long term relationship with someone as giving them owership rights to you either. I personally believe that the divorce rate wouldn't be so high if people didn't view their partners as a property and weren't placed in a situation where they feel like they've betrayed their partner if they even so much as consider what it would be like to have sex with someone else.
BTW- We
do have a 'proper' relationship- we have been together for 13 years (married for 10 of them) and I believe we have a stonger relationship for being completely honest with each other, treating each other with total respect as individuals and not feeling that we own each other.