The First Amendment forbids government to burden Americans' exercise of their religious beliefs. The Reynolds court came along and eviscerated this liberty. It said that states could itemize a list of religious activities which can be believed in but NOT practiced. Thus, Utah (and some neighboring states) could include polygamy as a conduct which could be criminalized.
So, in the wake of Reynolds, you could believe in polygamy to your heart's content (as Mormons do), but you could not practice it. The thoughts were just fine - the ACTIONS were not.
So, there are tens of thousands of Fundamentalist Mormons in the Intermountain West who eagerly embrace plural marriage in their minds. Utah residents who proceed to take a plural wife are presumptive felons (although the current Attorney General's office insists on NOT prosecuting them).
The prohibited actions (contemplated in Reynolds) occur when a man is married to one person and goes to bed with a different person (male or female). That makes you a felony bigamist. The 2003 Lawrence decision overruled that legislation, otherwise tens of thousands of Utahns would be in prison now for bigamy. So they can't prosecute the SEX. They have to rely on the other prong of the bigamy statute - the "purport" prong. You are guilty of bigamy if you are married to one person, and assert (believe) that you are married to another. Kody Brown has ONE legal wife. He THINKS of the other three ladies as "wives" in a religious sense, but the State has already said that having additional spouses is legally VOID and impossible. Legally, the other three women are girl-friends, mistresses, or just partners in an affair. So, Brown can call them "wives", but wives they are not.
As Jerryold Jensen points out in his reply, Kody's sexual activities with the various ladies are utterly shielded by Lawrence. It is the fact that Brown THINKS of them as "wives" that makes him a felon.
So now we have the unintended consequences of the Reynolds insanity. We have a state that REFUSES to prosecute the prohibited exercise (actions) of the believers, while it insists on criminalizing . . . . . . . . . . . .
THEIR THOUGHTS !!!!!!!!!!
Wait though! It criminalizes their lifestyle (existence and mindset) as did Bowers to homosexuals (until 2003), but the chief Mormon law enforcement officers of the state dare not prosecute it now for fear that someone like Kody Brown will come along and TEST the statute in the courts. The Church wrote the statute. Is it not the Church now who is frantically trying to salvage it? I wouldn't be surprised if those Lehi Keystone Kops have already been excommunicated for the biggest tactical blunder in modern Church history.
The following YouTube video is a Monty Python skit about church police. Skip to 00.36.