The "end of Christendom" in Canada?

Dramatic opening paragraph of a Globe and Mail (Canada) article, October 4:

 For the churches representing the majority of Canadian Christians, legalization of same-sex marriage will be a sign of the end of Christendom, the 1,700-year-old notion that has defined government in the Western world as devoted to the enforcement of Christian values, says one of Canada's leading theologians.

Later:

 There is fear that if, as widely expected, the [Canadian Supreme] court rules in favour of same-sex marriage and Parliament passes enabling legislation, churches will face persecution and discrimination in Canadian society for holding fast to the belief that God ordained marriage only for heterosexual couples.

From Roman Catholics and evangelical Protestants to Mormons, Muslims and Seventh Day Adventists among others, religious groups are also apprehensive that they may be stripped of their charitable status and other state benefits, penalized by public institutions, branded as hate-mongers and forced into accepting the legitimacy of same-sex unions.

It is the same fear that political scientists and theologians identify as driving the powerful conservative religious right in the United States -- a conviction that liberal, secular society is bent on erasing religion from public life.

Are their fears exaggerated?  What about similar fears that American evangelical Christianity may face the same in the future, perhaps in our lifetime?