Hi, Brian. Welcome to the site. I visited your website a few times before and it was great reading through it. I can tell that you're passionate about the subject esp. when I read your "decriminalizing of polygyny is essential" section, and that's good. Having to put up with the law in regards to polygyny is one thing but having to deal with fellow Christians who reject the clear truth of polygyny is another headache sometimes. We all may have our disagreements on what in the OT applies to or is still relevant to the NT or new covenant, but one thing that is clear is that the OT (particularly the Law) is very relevant in the NT for knowing what "sin" is, and the Law does not mention polygamy as a sin but as an acceptable practice. The Apostle Paul's letters that all Christians use a guide to know about the new covenant (NT) mentions,
Romans 3:20 Therefore by the deeds of the law no flesh will be justified in His sight, for by the law is the knowledge of sin.
Romans 7:7 What shall we say, then? Is the law sin? Certainly not! Indeed I would not have known what sin was except through the law. For I would not have known what coveting really was if the law had not said, "Do not covet."