Utter foolishness. What did Utah have to do to join the union? It had to outlaw polygamy.
Look, our natural rights derive from the Our Creator and his establishment of the Laws of Nature. While States are sovereign, a State that makes laws contrary to God's laws is rogue.
In a way the Civil War was about that theme. Chattel Slavery is immoral, immoral by G-d's Law. It was Christians who most opposed it in the US -- Quakers and religiously motivated individuals, including the both the most gentle of persons and the most forceful -- the meek to the bloody firebrands like John Brown.
Could a nation -- the North -- allow an slave nation to split off from it? The answer: no. That would have been immoral.
I'd rather have a discussion free from personal attack.
That said, the Utah Admission was a political event. There were no Federal Laws against polygamy...and there should not be. Ever.
If Utah or any other State decides they want to institutionalize polygamy they are free to do so.
Whether you like it or not, and I suspect you don't, we live in a Federal Republic where the Feds have no legal authority over the sexual behavior of it's citizens.