One husband, four wives and 17 children.

America knows them as reality TV stars on the hit show Sister Wives, but today they are unlikely legal crusaders in a fight over the fate of polygamy.

"I think that anybody should be able to organize their family according to how they choose," said Kody Brown.

It is an epic court battle, with Kody Brown and his wives against the state of Utah.

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They maintain theirs is a healthy lifestyle, where the wives have jobs, the children go to school, and everyone stands on equal ground.

But that is not how authorities in Utah see it. They threatened the Browns with prosecution after they flaunted their plural family on national television.

"I just want to be a free man," said Brown.

But opponents counter that women and children suffer in polygamist families.

One study by the Philosophical Transactions of The Royal Society reported that polygamy leads to "greater levels of crime, violence, poverty and gender inequality" and higher rates of "child neglect and abuse."

"The United Nations has said it's a violation of human rights and a violation of women's rights," said lawyer Marci Hamilton, the Paul R. Verkuil Chair of Public Law at the Benjamin N. Cardozo School of Law.

But the Browns say that's not how their family sees it.

They have distanced themselves from infamous polygamists like convicted pedophile Warren Jeffs, the president of the Fundamentalists Church of Jesus Christ of Latter-Day Saints. Jeffs had nearly 80 wives, two dozen of them under the age of 17.

The Browns say that's not what their family is like, nor any other polygamists they know.

"We just wanted to show people that we're normal," Christine Brown told ABC News.

In December, a federal judge sided with them, declaring a key part of Utah's polygamy law "unconstitutional." The judge ruled that the part of Utah's bigamy law forbidding cohabitation violated the First Amendment, which guarantees freedom of religion.

Co-habitation was essentially legalized, so Kody Brown can openly live with his four wives, Meri, Janelle, Robyn and Christine. They can openly call him their husband, just as long as there is only one marriage license.

The only marriage license Kody Brown has is to his first wife, Meri.

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"Thousands of people living plural marriage in Utah now are free," Kody Brown said of the ruling.

But opponents argue the decision will allow for more of the same secrecy that permitted Jeffs to claim young girls as wives without anyone outside the fundamentalists knowing.

The Browns counter that this ruling will actually help those women and children living in the shadows.

"This ruling would help create the check and balances that need to exist in societies that are closed now," Janelle Brown said. "Even if you want to leave, and you can reach out to government resource, which there exists, to say, 'I want to get out,' and there's not this stigma of where you're coming from."

Robyn Brown agrees, and she said she hopes the ruling will actually help women being exploited in the fundamentalist community.

"Say a girl is raped by her uncle and she's in the fundamentalist community - she's more concerned about taking this to the law, taking this to the authorities and having her family ripped apart than she is of actually being raped again," Robyn Brown told ABC News.

But lawyer Marci Hamilton doesn't believe that.

"They've got to be kidding," Hamilton said.

She says the ruling actually makes it tougher for authorities to investigate potential abuse.

"It's just very sad that we have a Hollywood polygamist family that has made it harder to protect the women in children in most polygamist families," Hamilton told ABC News.

As Utah's attorney general plans to appeal the first pro-polygamy ruling in 130 years, the Browns plan to stay in Nevada, where they have been living since Utah opened an investigation into their family.

"I don't think anything other than Utah is going to feel like home," Christine Brown said.

But for now, these reality stars say they're prepared to take their battle all the way to the Supreme Court.