A polygamous religious sect in southeastern British Columbia can't hide behind the Charter of Rights and Freedoms to defend a practice that oppresses women, victimizes children and harms society, a lawyer for the provincial government said Monday.

Craig Jones urged a B.C. Supreme Court judge to uphold Canada's 120-year-old law outlawing multiple marriage, arguing that two months of evidence from experts, former polygamists and current plural wives can only lead to one conclusion: polygamy is always harmful and must be stopped.

"This is what we know about polygamy both in theory and practice," said Jones.

"A polygamous society consumes its young. It arms itself with instruments of abuse and shields itself behind institutions of secrecy, insularity and control. It depresses every known indicator of women's equality. It is anti-democratic, anti-egalitarian, anti-liberal and antithetical to the proper functioning of any modern, rights-based society."

Watch now: Polygamy closing arguments

The government asked the court to examine the constitutionality of the polygamy law after the unsuccessful prosecution of two men from the sect in Bountiful, B.C.

Residents of Bountiful belong to the Fundamentalist Church of Jesus Christ of Latter Day Saints, a breakaway Mormon sect which, unlike the modern-day mainstream church, considers polygamy a sacred religious practice required to reach the highest level of heaven.

The controversy surrounding Bountiful has plagued police and lawmakers for two decades, as they struggled with the uncertainty of the law and whether it violates charter protections of religious freedom.

Jones noted the court heard from numerous experts who predicted multiple marriage will always lead to societies that control women, marry off young girls to older husbands and cast off young men. Most of those problems, the experts testified, were rooted in the limited supply of potential wives -- even if only a small portion of a society practises polygamy.

Testimony from women and children who left polygamous communities, as well as from women currently living in Bountiful, demonstrated all of those academic predictions were true, said Jones.

The court also heard evidence that girls as young as 12 years old were taken to the United States to marry much older men, including jailed polygamist leader Warren Jeffs.

Jones said the stories of young girls trafficked across the border and other allegations of abuse are no coincidence.

"The evidence in this case shows that these harms are caused by the practice of polygamy as surely as anything can be said to be caused by anything else," said Jones.

"These victims are inevitable, and there will be many more if the challengers succeed in making Canada the first western nation to decriminalize polygamy."

The court was asked to answer two questions: First, is the anti-polygamy law consistent with the Charter of Rights and Freedoms? Second, if the law is valid, what exactly does it prohibit?

Jones said the law doesn't violate the charter because constitutional protections don't extend to practices that are harmful.

To the second question, he said the law specifically prohibits multiple marriages involving one man and several wives, not the extremely rare practice of women with multiple husbands or same-sex polygamous relationships. On this point, the province disagrees with the federal government, which insists any form of polygamy is illegal.

Some critics of the law have argued polygamous marriages should only be outlawed if they involve abuse, coercion or exploitation. Jones rejected that argument.

"These societal harms are felt regardless of whether any particular polygamous relationship is good or bad," he told the court.

"These (harms such as abuse or exploitation) may be aggravating factors for sentencing purposes. A person who knowingly enters into a polygamous relationship is guilty."

The case will also hear closing arguments from the federal government, a government-appointed lawyer arguing against the law, a lawyer for Bountiful, and several other interveners, including civil liberties groups and women's rights advocates. The final submissions were streamed on the Internet and recorded for TV broadcasts after the judge granted a rare request from the media

Whatever Justice Robert Bauman eventually decides, it is expected the question will ultimately end up before the Supreme Court of Canada.

The province referred the issue to the B.C. Supreme Court after the unsuccessful prosecution of Oler and Winston Blackmore, who leads the other faction within the community.

The men were arrested in early 2009 and each charged with practising polygamy. A judge later threw out the charges because of how the province chose its prosecutor, setting the stage for the constitutional reference case.

Blackmore has boycotted the hearings, while Oler's side of the community has a lawyer in court.