Princeton Prof Alan Krueger lists five “urban legends” about terrorism for the Washington Post.

Here’s Myth Number 3:

3. Terrorists are likely to cross into the United States from Mexico.

This is a favorite chestnut of some activists and politicians keen to tighten immigration and build a fence on the Mexican border. But the historical record doesn’t bear it out. Of course, the past may not be a good predictor of the future, but terrorists have rarely crossed into the United States from Mexico. In a recent Nixon Center study of 373 Islamist terrorists, Robert Leiken and Steven Brooke concluded: “Despite widespread alarms raised over terrorist infiltration from Mexico, we found no terrorist presence in Mexico and no terrorists who entered the U.S. from Mexico.” By contrast, the authors found “a sizeable terrorist presence in Canada and a number of Canadian-based terrorists who have entered the U.S.” For example, Ahmed Ressam, the Algerian terrorist who tried to blow up Los Angeles International Airport in December 1999, was caught trying to cross the border from Canada into Washington state.

Hmm, that’s funny. That’s not what this guy says:

Texas’ top homeland security official said today that terrorists with ties to Hezbollah, Hamas and al-Qaida have been arrested crossing the Texas border with Mexico in recent years.

“Has there ever been anyone linked to terrorism arrested?” Texas Homeland Security Director Steve McCraw said in a speech to the North Texas Crime Commission. “Yes, there was.”

McCraw identified the most notable figure captured as Farida Goolam Mahomed Ahmed, who was arrested in July 2004 at the McAllen airport. She carried $7,300 in various currencies and a South African passport with pages missing. Federal officials later learned she waded across the Rio Grande.

According to federal court records, Ahmed pleaded guilty to improper entry by an alien, making a false statement and false use of a passport. She was sentenced to time served and deported to South Africa. Other details of the case were sealed.

But on Wednesday, McCraw described Ahmed as having ties to an insurgent group in Pakistan and whose specialty was smuggling Afghanis and other foreign nationals across the border.

McCraw also said that since March 2006, 347 people from what he called “terrorism-related countries” have been arrested crossing the border in Texas. The number of Iraqis captured at the border has tripled since last year, he said.

Don’t forget that Farida had a buddy, also a South African, arrested in Mexico about the same time. And of course it was a long time ago, but that’s how the Duka brothers–of Fort Dix Six fame–came into the country as well.

4. Terrorism is mainly perpetrated by Muslims.

Wrong. No religion has a monopoly on terrorism. Every major religious faith has had followers involved in terrorism. (Sri Lanka, for instance, has grappled for decades with the Liberation Tigers of Tamil Eelam, a separatist group that pioneered suicide bombing as a terrorist tactic and hopes to create a homeland for the country’s mostly Tamil minority, who are largely Hindu.) Although radical Islamic terrorists are the worry du jour because of 9/11 and Iraq, the data show pretty clearly that the predominant religion of a country is not a good predictor of whether its people will become involved in terrorism.

He goes on to mention McVeigh, and point out that most terrorism is local. And he’s technically right, if you consider exactly what he says: countries like Colombia and Peru are Catholic and have their people involved in terrorism–so if you look at all such “nations involved in terrorism” you can reach the answer he gives.

It’s also a question of the sample size: if you think about the last few decades and think about how many of the incidents were committed by the People’s Revolutionary Army of Wherever, the global rise in Islamist terrorism fades into the background. But the recent frequency, scale, and violence of such incidents suggest that something has changed in the world that has spurred militarized Islamists to engage on terrorism on a global scale.

We’ve also been preventing who knows how many of Islamist terror attempts that never make it into Dr. Krueger’s statistics.

Statistics aside: even if he’s right about worldwide numbers, so what? Common sense says that if you live in Sri Lanka, the Tamil Tigers are a daily threat to individuals and to the polity. But for most readers of the Washington Post, especially those in the Pentagon, the threat comes from a fairly obvious, well-publicized, not-at-all counterintuitive direction.

Sometimes, you know, the conventional wisdom gets it right.

(hat tip to Patterico’s DRJ for the McCraw article.)