Across Canada, people of goodwill are cringing as Quebec's identity debate turns toxic. Premier Jean Charest served blunt notice this week that politicians are "fanning the flames of intolerance" toward cultural and religious minorities, and promoting a "siege mentality." That may sound alarmist to those who have not followed the debate. But Charest had reason to speak out. And not a minute too soon. Consider Quebec's two opposition leaders. Mario Dumont of the Action Démocratique party argues that Quebec is "pretty much at capacity, in terms of intake," and wants to block increases in immigration. Parti Québécois Leader Pauline Marois,...