i think the problem here is that despite a whole lot of words spoken... someone almost always does get hurt. I have friends who cling to the idea that it COULD work depite many many years of pain and disapointment.
The only time I've ever seen a polyamorous thing work was when there was no romantic love at all. Merely friendship with sex. Even then, it was swimming in dangerous waters! There was some hurt involved, but it was fairly minor... especially compared to the level of pain I have routinely seen in these relationships.
There is also the exponentially increasing risk of disease from each additional party involved... I think it is a bad idea, but I don't think I need to live other people's lives for them. I do feel sad when I see my friends repeatedly hurting themselves, but I try not to judge. If that makes any sense.
~Witch