With all eyes glued on the UN Security Council in February 2003, then U.S. secretary of state Colin Powell laid out Washington’s case for invading Iraq — based on top-secret intelligence purporting to show Iraq had weapons of mass destruction.

As we now know, Powell would have been just as accurate making the case for the existence of the tooth fairy.

The eventual revelation that there were no weapons of mass destruction in Iraq should serve as a constant reminder of the hazard of simply accepting at face value evidence gathered from the shadowy world of intelligence sources.

Such evidence is notoriously unreliable, coming from unidentified sources whose knowledge or motives are unknown, or who may have simply confirmed “information” put to them by interrogators in order to end a particularly excruciating bout of torture.

And yet Canadian immigration law allows our authorities to use such evidence — unchallenged — to detain indefinitely an immigrant or refugee claimant they believe might pose a security threat. The Harper government last week defended the government’s right to detain people on immigration “security certificates,” arguing before the Supreme Court that such sweeping powers are necessary to protect Canadians against terrorism. Five Muslim men have been held in Canada under these certificates for the past few years.

But surely the best means of protecting ourselves, not to mention our democracy and the rights of the accused, lies in learning the truth.

The system of security certificates makes it very difficult to learn the truth. Under the system, the accused are tried in secret courts. Neither they nor their lawyers are permitted to know the evidence against them, making it impossible for them to challenge this evidence, whatever it might be.

Criminal lawyer Marlys Edwardh notes that this means the judge must weigh the evidence, without any way of knowing the weaknesses in the government’s case.

The government may, for instance, argue that an accused was at an Al Qaeda training camp at a particular time. How can the judge challenge this, asks Edwardh: “What can he say: Are you sure?” Meanwhile, the accused is denied the opportunity to present evidence that may show he was fully employed in Canada at the time and, therefore, couldn’t have been at the training camp.

It’s often asserted that, in these cases, there’s a clash between the goal of protecting civil liberties and the goal of ensuring the safety of Canadians. But wrong information about terrorist threats does nothing to ensure our safety. Indeed, wrong information can lead us to confuse real and imagined terrorist threats — with possibly dangerous consequences.

Is there any evidence that the American people are safer because they invaded Iraq, out of the false belief that Iraq had weapons of mass destruction?

If Canadians join U.S. wars — prodded by fears of terrorist plots that may not even be true — it’s hard to see how this makes us safer. It might well do the opposite.

Linda McQuaig

Journalist and best-selling author Linda McQuaig has developed a reputation for challenging the establishment. As a reporter for The Globe and Mail, she won a National Newspaper Award in 1989...