This article about same-sex marriage.  In the lede, the issue of same-sex marriage is said to be a human rights issue, an equality under the law issue, a political issue.  The article says marriages are legal and social institutions.  The article then goes on to explain why some favor changing the law to recognize same sex marriage, and it explains why some oppose changing the law to include same sex marriage.  
I don't see why a lawyer, a law professor, a politician, a judge, a law review article etc would not be considered an expert on the subject (if not they then who).  Also, the entire issue of being an expert was in regards to Self Published Sources only (Wikipedia states that a SPS may be used if the author is a recognized expert).  None of the citations are SPS  and if they were they are still experts.
As I have told you law review articles are easily accessible due to the wonder of the internet, and I highly suggest you follow you own advice and read the citations above (and yes to answer your question I have verified the articles).
I don't know if you're going to object to online news articles, but this is more for your own personal edification, Nat Gertler, to help you understand that argument of incest to polygamy is an argument that is being made. (They are non-US for your pleasure) Please remember we are considering sources for the purpose of demonstrating that this is an argument that is being made.  We are not evaluating the argument or criticizing the argument. http://www.pinknews.co.uk/2009/11/27/australian-gay-marriage-could-lead-to-incest-and-polygamy-religious-figures-say/
http://www.lifesitenews.com/ldn/2009/jan/09012207.html