Canada's ban on polygamy is an unconstitutional law rooted in religion that persecutes the rights of the very women and children the government claims to protect, a lawyer told court Wednesday.

But his argument came on the heels of an opposing view from an advocacy group lawyer who said quashing the law and permitting multiple marriages would violate Canada's international human rights obligations.

The question of whether the ban on polygamy violates religious freedoms has been referred to a judge after British Columbia abandoned its prosecution of two religious leaders in Bountiful, B.C.

The obscure, breakaway Mormon sect in southeastern B.C. is being used as a case study to determine whether polygamy is a protected religious practice or a crime.

The provincial and federal government each support the law. The court has appointed veteran lawyer George Macintosh as an amicus to argue the other side.

Macintosh said opponents of polygamy paint the wives in polygamous marriages as "brainwashed" women who would be desperate to leave if only given the option.

He said that's not true, and promised the court will hear from women living in Bountiful who are happy with their lives.

"Women in polygamous marriages actually want to enter into them and they're fully capable of doing so, in the same way that many men and women enter into monogamous marriages," said Macintosh.

"Many women in Bountiful were born into the FLDS (Fundamentalist Church of Jesus Christ of Latter Day Saints) religion, which celebrates polygamous marriage. These women grew up believing that this is the best way to live. You'll hear from some of them, and I suspect you'll conclude they are sincere and heartfelt."

Macintosh said the governments of today are using a "modern, progressive" argument about women's rights to defend the law, when those concerns were likely far from the minds of politicians 120 years ago when the law was drafted.

"Section 293, in 1890, was instead about stopping Mormons and aboriginals, because a Christian marriage was, in 1890, a monogamous man-woman union," said Macintosh.

Opponents of polygamy have cited a long list of abuses they say are inextricably linked to polygamy, including child brides, teenage pregnancy, sexual abuse of girls, the subjugation of women and casting away boys who aren't able to marry.

Macintosh replied that if there are abuses associated with polygamy in Bountiful or elsewhere, the government should focus on prosecuting those crimes rather than targeting a type of relationship that isn't, by itself, abusive.

And he pointed out that the current law targets anyone who enters into a polygamous relationship, regardless of their sex.

"When there are abuses of whatever kind, whether they are in a monogamous setting or a polygamous setting, there are laws in place to address the harmful conduct, whether it is spousal or child abuse or some other harm," he said.

"Under (the law's) wording, you're just as guilty of polygamy if you are one of the women as you are if you are one of the men."

Earlier in the day, the court heard from a lawyer representing the Canadian Coalition for the Rights of Children and the David Asper Centre for Constitutional Rights, who argued lifting the law against polygamy would violate Canada's international obligations.

In particular, Brent Olthuis said the UN Convention on the Rights of the Child requires the Canadian government to protect children from the harms that are associated with polygamy as practised in Bountiful.

Olthuis said polygamy puts girls at risk of physical and sexual abuse, denies them the right to consent to sex or marriage, and deprives them of reproductive health care.

He also said boys in such communities are often removed from school before graduation to work for little or no pay, and are only permitted to marry a girl or women chosen by the church.

Olthuis said both the Charter of Rights and Freedoms and the UN convention require Canada to prevent such abuses.

"Any practices that are exploitive or otherwise harmful to children are themselves inconsistent with the values that are enacted under the Charter (of Rights and Freedoms) and inconsistent with the convention," said Olthuis.

Another group opposed to polygamy, the Christian Legal Fellowship, urged the court to uphold the law because allowing multiple marriage would undermine the institution of marriage.

"We will show that polygamy, in a sense, is a fraud upon society," said Gerald Chipeur.

"It is a fraud on the public because it deprives the public of the social and economic predictability associated with the current social and economic realities related to the definition of marriage as a conjugal union of two persons."

Last year, the two leaders of Bountiful, Winston Blackmore and James Oler, were each charged with one count of practising polygamy, but those charges were thrown out on technical legal grounds.

Several other interveners presented Wednesday both for and against the law, including the Canadian Association for Free Expression.

The association's lawyer, Doug Christie, has represented a number of controversial figures, including Holocaust denier Ernst Zundel and aboriginal leader David Ahenakew, who was acquitted of hate speech charges after comments he made about Jews. The group's president is Paul Fromm, a former Ontario teacher who was fired from a Toronto-area school board because of his association with neo-Nazi groups and attendance at white supremacist events.

Christie said his group is opposed to the law, which he says is an example of government interfering with the freedom to practice religion.

"The intrusion of the state into religious belief is very dangerous," said Christie.