"Canada is not Mexico," the U.S. homeland security secretary said this week, before explaining that Canada is, well, sort of like Mexico.

Janet Napolitano cut her teeth as a politician in Arizona, where the top issue is almost always border security. On the other side of the walls that separate her state from Mexico, gang violence is always pushing north.

That seems to have molded her ideas about what a border should look like -- a barrier to keep out threats, no matter whether it's in Nogales, Mexico, or Windsor, Ont.

"Yes, Canada is not Mexico, it doesn't have a drug war going on, it didn't have 6,000 homicides that were drug-related last year," she said.

"Nonetheless, to the extent that terrorists have come into our country or suspected or known terrorists have entered our country across a border, it's been across the Canadian border. There are real issues there."

When a reporter asked if she was referring to the 9/11 terrorists, she answered: "Not just those but others as well."

Our readers were outraged. How could the person responsible for U.S. border security think the 9/11 terrorists entered the U.S. from Canada? Didn't we correct that myth years ago? She later said she had been misunderstood.

"I know that the September 11th hijackers did not come through Canada to the United States," Napolitano said in a statement. "There are other instances, however, when suspected terrorists have attempted to enter our country from Canada to the United States. Some of these are well-known to the public -- such as the Millennium Bomber -- while others are not due to security reasons."

That did little to pacify our readers, who were outraged that Canada had been partly blamed for the worst-ever terrorist attack on U.S. soil.

"A Former U.S. Citizen" wrote: "Paranoia has been, for a long time, (anyone remember the McCarthy era?) such a crippling disease which will ultimately led to the demise of a once great country. You know they do have medications to treat such disorders... I suggest they all take a handful then work on their own problems."

The problem wasn't helped when U.S. Sen. John McCain -- who represents Arizona, of course -- defended Napolitano's earlier comments.

"Well, some of the 9/11 hijackers did come through Canada, as you know," McCain told Fox News last Friday, after Napolitano had said that was incorrect.

"Dave Boyle of Ottawa" wrote: "During the U.S. election campaign, I thought McCain came across as a breath of fresh air for the Republican Party. At last, I thought, an urbane and intellectual leader for the Republicans. I was obviously in error. Thank goodness, Obama won instead of him."

But others said that while none of the 9/11 terrorists passed through the Canada-.U.S. border, Napolitano was right about the would-be Millennium Bomber, Ahmed Ressam, who crossed over from Victoria, B.C., to Washington state in 1999. He was captured on the other side of the border.

"Clean up our act first Canada" wrote: "The FACT is we have many terrorist cells operating within Canada... that's a fact. Whether or not others have permeated the border isn't public knowledge."

"Heather in Ontario" wrote that even if terrorists are crossing the border, it's still the fault of the Americans because it's their job to stop them. That seems a bit like blaming someone for walking into your fist, but it's an accurate point.

"Last time I checked, when you're crossing from Canada to the US, it's the US Border Guards who have the job of stopping you, not the Canadian ones! So if this situation does exist, how exactly is it our fault?" she wrote.

That brings us back to Napolitano's initial thought: tougher security is needed. And that's the problem. It will slow down border crossings, which in turn will hurt businesses that rely on quick and easy access to the U.S. or Canada.

Every day accounts for roughly $1.5 billion in trade between the two countries, as more than 300,000 people cross the border.

"Edmonton John" wrote: "This is very troubling. I have no problem with a proactive, intelligent security system. However, when the head of the security agency displays such ignorance, one can only surmise that the system is riddled with misinformation. The consequence will inevitably be inefficiency in our cross-border dealings as the US compensates for the deficiencies in their knowledge."