It might appear so, but a friend of mine who's in a poly relationship gets harassed fairly frequently on OKC because she's married.
I'm not saying it didn't happen... but it might be kind of like saying "planes aren't safe, I had a friend that was in a plane crash."
I'd imagine how welcoming people are to others in poly relationships largely depends on where you are. People in El Paso, TX (where my friend and I live) are likely less open to that sort of thing than people elsewhere.