DY: Why is it a CH if the State and the IRS couldn’t care less if you live with a woman, have children, but never get married. (In fact, you will make the IRS happy by doing so.) You simply asserted it is a CH, but you are wrong as it is not, and can even be a Kiddush Hashem. (If you are not registering it as not to violate the archaic polygamy laws on the books and to help a girl who needs to get married have a husband.)
RAM has many many tapes, but IY”H I will find the one (at least one) that he indicates he has no opposition to it. (I didn’t say he was “calling for it”. But the Vilna Gaon WAS calling for polygamy, and I can try to find that source too if you’d like. And Rav Ovadia Yosef shlit”a is another proponent of allowing contemporary polygamy.)