People champion polyamory for the same reason poor people vote for people who run on platforms designed to fuck them over. They just imagine that one day, they'll be the one benefiting, when truth be told, the vast, vast majority of them would be the ones sitting at home trying to convince themselves they did the right thing. It's a rush to be more progressive than though. I mean, that thread has people asking the guy who got cheated on what he did wrong. Because it can't be her fault for cheating, obviously.