I am in a committed three-person relationship. There is a difference between Polygamy and Polyamory. Polyamory is a romantic relationship between more than two people. Polygamy is marriage between more than two people and that is the one that is illegal.
There are many problems which include not everybody being able to be on the same spouse's health insurance, since the health insurance we're on only covers one spouse or domestic partner. So that is just one example where not everybody in the relationship ends up being treated equally in the law. Imagine what it's like having to negotiate who gets to have the same benefits as the rest.
I'm openly polyamorous and we even had a traditional wedding (four years ago) with the three families and with cake and an officiant and catering, and we wear rings. I have never experienced weird looks by anyone, and nobody has ever shared an opinion that sounded negative. For example, I have never been told that I'm wrong or unnatural. So I don't know about the people you talk to but it seems those reactions tend to come from people who are young and making judgments about things is what young people do in order to try to make the world make sense. It is large and chaotic and confusing. Some will figure out that it doesn't all have to make sense (the smart ones).
People almost exclusively react with curiosity. Moms and dads, our neighbors, christians, catholics, classmates, and coworkers. But the curiosity is only brief and life goes on as if the fact is completely forgotten. Because as it turns out, who I choose to be with is not that big a deal to other people at all.
I had a professor who once said she was concerned about my workload during one term in college, but then she told me it's a good thing that I have two people who can take care of me at home.
P.S. The thread title is nonsense. Homosexuality and Polygamy are apples and oranges. What does polygamy have to do with homosexuality? Polygamy is a kind of family, homosexuality is a kind of sexuality, which is about who you like to rub slippery bits with. If you want to talk about same-*** marriage, call it "gay marriage" or "same-*** marriage". Then you would be comparing apples to apples.