Because we didn't learn anything from it the first time around.
The Canadian Security Intelligence Service, Canada's principal intelligence agency, routinely transmits to U.S. authorities the names and personal details of Canadian citizens who are suspected of, but not charged with, what the agency refers to as "terrorist-related activity."
The criteria used to turn over the names are secret, as is the process itself.
Our "principal intelligence agency" doesn't work for us; it works for American intelligence agencies.
In at least some cases, the people in the cables appear to have been named as potential terrorists solely based on their associations with other suspects, rather than any actions or hard evidence.
Of the 41 people named, 21 do not appear to have ever been charged, and some had never come to the attention of the Americans before being named by their own government.
This isn't old news; it's based on leaked cables from WikiLeaks that cover a period from 2009 to 2010. And while the United States may be our ally, it's also the same country that has been running show trials posing as military tribunals, legalizing indefinite detention without due process, torturing one of its own who has yet to be convicted of a crime (see Manning, Bradley) and attempting to murder another who has never even been charged (see al-Alwaki, Anwar). If the American intelligence and law enforcement agencies will treat American citizens that way, imagine what they'll feel free to do to citizens of another country who have been designated as suspected terrorists by agents of their own government.
Remember former CSIS Director Jim Judd whining in public about the way citizens didn't show enough deference to agencies like his? Perhaps he'd like to tell us again why we should have more respect for an agency that will sell its own citizens out to a foreign government based on nothing more than guilt by association.