The issue of polygamy is unrelated to gay marriage. I am really eager to see how Winston Blackmore can wind the two together. He argues "the Canadian definition of marriage, which includes same-sex couples, should then also include multiple partners."
Gay marriage is about civil law and what the state is willing to recognize as a union. Polygamy, however, is bound up with religion. To be more strict polygamy doesn't even exist outside of a religious context, yet. If we were to take this scenario to an extreme, Blackmore could win the case that he is arguing and get recognition for all of his 19 civil wives, yet still be a criminal for having more than one religious wife.
This is, of course, absurd. We are so close to this absurd outcome because Blackmore is skipping a step. Before the state recognition of civil polygamy comes the decriminalization of religious polygamy. And this is not hard to argue.
There is a space in between, or rather outside of, civil and religious unions. For lack of a better term, let us call these 'secular unions'. These are unions not recognized by the state or the church. A man in such a union may do as he wishes. He may take another partner, and another, and another, and 19 or more other partners. He may do so with no charge of criminality. Only when he tries to create the same union under the guise of religion does it become criminal.
The Canadian Charter of Rights and Freedoms guarantees the freedom of religion. As the law stands, a secular man may do things a religious man cannot. How much closer to the definition of religious persecution would we have to get before 'foul' were called.
In stead of making this argument for religious freedom Blackmore chooses absurdity. And he is free to do so.
Link: Accused polygamist to use gay-marriage laws as defence