I think polygamy should be regulated in the US. BoP rests on those who wish to take people's freedom away.
-It is religious freedom since some people's religion allows them to marry multiple people. Some non religious people would also do it because they want to.
-It is not for everybody, but it is for some people.
-It enables smarter people to marry more people, and as a result, they can produce smarter kids, making a better society not just from genetics, but because smarter people raise smarter kids by teaching them how to become smart.
-It can solve the STD epidemic in the US if we require polygamous people to get their STDs treated before they go polygamous. From there, if it greatly reduces STDs, then there would be less STDs as well as a huge creation of jobs because people would be treating the STDs.
-It requires the enthusiastic consent of all spouses.
Now onto rebuttals that I thought of:
-The claim that it would cause crime rates to go up. In societies where the crime rate is higher, this is because of poverty and not the legalization of polygamy. Moreover, Ethiopia, where polygamy is banned, has a comparable murder rate to the average of it's neighbors which have legalized polygamy. In western Africa, countries that banned polygamy have a higher murder rate than countries that legalized it.
https://metro.co.uk/wp-content/uploads/2015/06/ad_173236258.jpg?quality=80&strip=all(legality of polygamy)