We have a court decision in Utah that throws out the ban on polygamous cohabitation (but not bigamy that is a result of deception) based on the similar court case wherein the Supreme Court stated that it was unconstitutional for a federal law to define marriage as being exclusively between a man and a woman. Slippery slope arguments against redefining marriage appear to be born out. Slippery slope arguments are frequently considered a logical fallacy but not always. Marriage will come to mean whatever someone says it means going forward and therefore meaningless.
The toleration of polygamy is a terrible idea. Long term it will lead to many males being social outcasts and high status males acquiring “harems”. History has shown polygamous societies to be unstable. The building of civilization is slow but collapse comes quickly.