Utah was not allowed admission to the Union until 1896, long after it had enough population to qualify. It was only when it (and the Mormon church) outlawed polygamy that Congress agreed to admitting it.
But, as a nation we weren’t as ‘enlightened’ then as we are today. Who are any of us to pass any kind of judgement on alternative lifestyles? Men can ‘become women’ just because they feel like it. It’s the women who object to pretend women who are to be shunned, not the pretend women.
We are living in crazy times and God help those who try and point that out.
The reason the Republicans felt as strongly about abolishing polygamy as they did about slavery is because people in the United States who had the opportunity to actually observe the practice, found that it led to conditions no better than slavery for the women. But what did they know, right?