The first mention of plural marriage in the Bible is of one of the patriarchs who was an evil man (Genesis 4:19-23). Thus, it is claimed, polygamy is evil.
By the same token we can claim that nobody ever passed urine or stools until the days of Eglon in the Book of Judges because nobody is ever described as urinating or defecating until then. Furthermore, it can be 'proved' from the Bible that people only ever urinated against walls since that is the only method that is mentioned in the Bible (though you'll only find it in the KJV since for some reason modern Bibles find it too embarrassing to include):
"For the whole house of Ahab shall perish: and I will cut off from Ahab him that pisseth against the wall, and him that is shut up and left in Israel" (2 Kings 9:8, KJV).
The fact that Lamech is the first named polygamist in the Bible doesn't mean that he was the first one or that the practice is evil. If it was evil, would Yahweh legislate in favour of plural marriage in His Law (Torah) or tell David that He gave him his wives?
We see that in order to advance such a proposition the anti-polygamists must grasp at straws.
