Sloppy summary of Utah history.
First - polygamy was illegal the entire time it was practiced
Second - Young didn't want to be a territory of the US - he sought to establish his own separate country of Deseret - a theocracy. And continually chased and harassed government officials sent there by DC to oversee the territory.
Third - Young was brutal towards those who disagreed with his rule and many were killed under his approval as 'apostates'
Finally (though there are many other points) they purposefully hid their polygamy - payed lip service to it for statehood - only to be called on the lies and require a second manifesto to be written denouncing it. Infact, mormon church felt that polygamy could continue in countries neutral to it at the time (Canada and Mexico) - wanting to have their cake and eat it too.
How would you like DC to tell you what you can and can not practice in your religious belief system?
LOL, tell that to the pagans who aren't allowed to sacrifice animals guitarplayer. Smith started polygamy - it was illegal by both statutory law as well as mormon church law. If it realllllllly was true, then the mormon church should never have had it's "manifestos" telling its members to follow the law of the land and not the law of "god".