I think I understand why people hate on them. First, cheaters in monogamous relationships. What people don’t realize is that there are cheaters in Poly relationships to. It’s actually a ton of extra work making sure everyone and their wishes are respected.
Second, religious fundamentalists. People think of Mormons mostly when thinking of Poly people. Misogyny, religous indoctrination, all the worst shit you can think of. Not all Poly people are religious you know.
Polyamorus people deserve marriage equality. They deserve to love the way they want.