While I'm sorry that your friend didn't take your revelation well, I have to agree with the others. You did come off as preachy, and you got your "facts" wrong. While, yes, many cultures did practice a type of polyamory there were others that practiced enforced monogamy. The Roman Empire for example.
I recently came out about polyamory to all of my close girlfriends, only one of them seems to be taking it in stride. The others are pretending it doesn't exist. I just told them, "Hey, this is what Bear and I are doing." so that when I talk about Lovely they won't wonder who and what I'm talking about.
I did not, however, try to convince them that one way is more right or wrong than the other. It's just different.
Give your friend a few days to process what you have said, apologize for being preachy, and see if you can go on from there.
Pinky, 41, f, bi. Married to Bear, 42, m, straight.
Not dating anyone right now.
I became insane with long intervals of horrible sanity.--EAP