 They thought that they had been blessed with several life partners, and it seemed wrong to elevate one relationship above all others. They didn't like the blood-soaked sexist history of marriage, which goes back to Mesopotamian law where men – they don't own women. That's wrong. They own their reproductive and sexual capacities. I could go on. Some people simply didn't think they were monogamous. They wanted to live with someone and have consensual non-monogamy.