Polygamists tend to rely on the welfare system to support their (sometimes very) large families. In that way, polygamy hurts every taxpayer.
AFAIK, even Islam (and “orthodox” Mormonism) requires that a man be able to support his family, before being allowed to take multiple wives.
The rules against polygamy might have worked, back when extra-marital sex was illegal. How can we punish a man for polygamous marriage, when we wouldn’t punish him for adultery? It’s a tangled web, indeed.
How is a guy with 10 baby mammas in 10 different houses receiving welfare better than a guy with 3 wives, one of which might get food stamps?
Are you talking about urban and promiscuous ethnic folks or are you referring to secretive and insular FLDS types? Because the FLDS adamantly refuse social services and the social workers that come with accepting the King's Coin.