my opinion is based upon what polygamy is not what you think it is. Again poly and polygamy are not the same lifestyles and there is more to it than the marriage aspect that you keep throwing out there. here since you are having such a hard time, here is a link that may help.
http://www.yourtango.com/experts/mr-mike-hatcher/polyamory-vs-polygamy-what-difference-between-two
I don't know who this Mike Hatcher is but he obviously does not know what he is talking about when it comes to polyamory.
His article is so filled with qualifiers that it means nothing.
It is also worth pointing out that whilst polygamy is often linked to religion, the same cannot be said about polyamory.
Polyamory is often linked to the Pagan religions like Wicca.
polygamy does tend to only refer to the act of a man having more than one wife and it is, therefore, based on gender.
That might be how you and him are used to hearing about it but that is not mean that is all it is. I'm used to only hearing about bacon in reference to eggs, but that doesn't mean BLT's don't exist.
polymory can of course involve people of the same sex as well whereas this won't be possible with polygamy due to its strong links to religion and culture.
There are many religions that allow same sex marriage. Once again he is trying to narrow it down to something done by Mormonism and Islamic religions. Other religions allow both same sex marriage and polygamy. Most Celtic religions, Buddism, and even Hindism (even if India outlawed it).
It is also generally true that polygamy has a tendency to last longer like normal marriages, but with polyamory it is more about the moment and living in it and this means it may last for weeks, months or even years depending on the people involved which is similar to swinger couples or open relationships.
Here his lack of knowledge really shines through. Polyamory means many loves, not many fuck buddies. Poly relationships tend to last a long time. They tend to be marriage like. Yes, sometimes they end, just like any relationship, and there is a dating process with lots of failed relationships, but poly relationships are not about the moment like swing relationships are.