I think something you're failing to consider is the highly variable and sporadic nature of terrorism. Yes, drunk driving has historically killed more Canadians, but it is a relatively static and well understood threat. The exact rate may slightly shift up or down year to year, but there's no credible reason to think a lack of vigilance could cause the drunk driving fatality rate to explode to a hundred or a thousand times its current value next year. By comparison, the threat of terrorism is not nearly as predictable or regular. A few motivated individuals with access to explosives or restricted firearms could cause hundreds or thousands of fatalities in a single event. This type of event may not have precedent in Canada, but it's happened several times in the last couple decade to our political allies, so I think the threat warrants more vigilance than our fatality count would suggest.