Canada's ban on polygamy unfairly criminalizes healthy relationships involving multiple spouses, a lawyer representing the Canadian Polyamory Advocacy Association told a special hearing in B.C. Supreme Court on Wednesday.

The group is among several interveners in the landmark constitutional case in B.C., which was prompted by allegations of abuse in the isolated religious sect of Bountiful, B.C.

But the group's lawyer, John Ince, said the shocking stories that have emerged from Bountiful don't reflect the lives of hundreds of polyamorists across Canada, who say their relationships are secular, egalitarian and are part of mainstream society.

He said that's why the provincial and federal governments have largely ignored polyamory in the complex discussion of polygamy, and have offered no evidence that polyamory causes anyone harm.

"There's been a dearth of evidence in this case respecting polyamory -- I guess they [the governments] are avoiding attracting to their Achilles heel," Ince said during his closing arguments.

"There is no evidence of harm that justifies the criminalization of polyamorist families."

Lawyers for the provincial and federal governments have offered contradictory opinions on whether multi-partner relationships outside of a religious context would be illegal under the law.

The B.C. government suggested polyamorists may be included in cases involving men with multiple wives, but not women with multiple husbands or same-sex relationships.

The federal government has said polyamorists would only be covered by the law if they have a formal marriage ceremony.

The governments have also argued it would be impossible for the law to distinguish between "good" and "bad" polygamy.

Ince said it was difficult to pinpoint exactly how many polyamorists there are in Canada, but he noted the association conducted a survey and received 560 replies from people who said they were living with multiple partners in polyamorist relationships.

They include men living with multiple women, women with multiple male partners, and same-sex relationships, said Ince.

He compared that with roughly 100 practising polygamists estimated to be living in Bountiful, out of a total population of about 1,000 in that community.

Ince's group filed written affidavits from several polyamorists across the country, who described happy families, sometimes with children, where spouses are equal, and resources and duties such as childcare are shared.

"All of this contrasts dramatically with the type of multi-partner conjugality that has been the focus of this case, which is patriarchal polygamy," he said, referring to Bountiful.

"It is that patriarchal polygamous style of multi-party conjugality that was known to the lawmakers in the 1890s. They could not anticipate the development of the post-modern institution of polyamory."

If the law is upheld, said Ince, polyamorists feel they will be under increased scrutiny from law enforcement, child welfare agencies and immigration officials.

Ince suggested the law could be changed to exclude multi-partner relationships if the participants express a belief in gender equality. For example, a relationship structured in a way that the husband is allowed multiple partners but his wives are not would be illegal, said Ince.

He asked the court to throw out the current law and send it back to Parliament.A lawyer for the B.C. government has previously rejected Ince's suggestion, arguing it would be too easy for a harmful polygamous marriage to avoid scrutiny simply by publicly professing a belief in equality.

The case was prompted by the failed prosecution in 2009 of two men from Bountiful, where residents follow the Fundamentalist Church of Jesus Christ of Latter-day Saints, or FLDS. Unlike the mainstream church, the FLDS still practises polygamy.