Incest is a practice with severe genetic consequences to potential offspring. I don't think it should be outlawed but cautioned, especially with direct relations. Asian countries like Japan have much less strict laws regarding that issue.

Polygamy is a thing that happens already in society. People are promiscuous and have multiple partners often. Polygamy and by extension polyandry should not be confused with polygamist colonies as the colonies don't give the people living within them a choice to live whatever lifestyle they want.