LDS polygamy question on D&C verses?

I'm not a Latter Day Saint (by name), but reading the bible about 10 times, and studying Roman and Jewish history, I've come to the conclusion that there isn't anything immoral about Polygamy. The Roman government is the one who made it immoral because they wanted to control the Jewish population who were most of them Polygamist. They believe by controlling the Jewish population, they would preserve national security. You ask, what is adultery then? Adultery simply is a commandment from God not to have with another man's wife. A man could have more than one wife, just not the other way around. Now if a man puts away his wife (divorce) with a certificate, then she is free game according to what God told Moses in the bible. He did this because he knew the natural instinct of man was jealousy which leaded to murder, discourd and other terrible things. Another thing, if a woman get's pregnant, she becomes the man's wife indirectly. Now that we have these "gay" marriages, there might be a few polygamist that will argue that if the gays can get married, then a man should have more than one wife.