The communities that practice polygyny are doing it right now, regardless of the law. It can be pretty brutal, but so can monogamous marriages, and they should be treated the same.
Domestic violence should be (and is) illegal, and no one should be forced into marriage against their will. In practice, of course, people are going to be indoctrinated from a young age, misled, and pushed into marriage (polygamous or not), and we should find ways to stop that. Banning certain types of marriage is an ineffectual method, because polyamory is unenforceable.