You can try the Joseph Smith card but back then it was legal and times were very different. Nobody gives Edgard Allen Poe **** for having a 13 year old wife.....who also happened to be his cousin.
That's like saying its ok to keep a black kid in your basement and make him clean your house for free because the President's did it 200 years ago.
He's saying it was never okay, not the other way around. Have you ever had an IQ test done on you?