Racial profiling is an ugly business -- and I have been on record opposing it for years. But I'm not opposed to allowing -- no, requiring -- airlines to pay closer attention to passengers that fit a terrorist profile, which includes national origin. The problem is distinguishing between what is permissible, indeed prudent, behavior and what is merely bigotry. As the Christmas day incident involving an Arab American Secret Service agent who was denied passage on an American Airlines makes clear, it's not always easy to tell the difference. Racial profiling entails picking someone out for special scrutiny simply because of his race. It happens when highway patrolmen pull over blacks who've committed no traffic violations for spot checks but ignore other drivers who share similar characteristics, say out-of-state plates or expensive cars. It happens when security guards at a mall tail black customers in stores or insist on inspecting only their bags, ignoring whites. The underlying presumption in these cases is that blacks are more likely to be involved in criminal acts because of the color of their skin. This kind of racial profiling is both morally wrong and ineffective. But there are times when it makes sense to include race or national origin in a larger, criminal profile, particularly if you're dealing with a crime that has already been committed or is ongoing and the participants all come from a single ethnic or racial group. It would make no sense if witnesses identified a six-feet-tall, blond male fleeing a homicide but police stopped females, short men, or blacks or Latinos for questioning. Likewise, if you stopped every tall, blond man, a lot of innocent people would be inconvenienced, if only temporarily. Which brings us to the case of the Arab American Secret Service agent. Walid Shater was allowed initially to board an American Airlines plane in Baltimore headed for Texas, carrying a loaded gun, but then was pulled off the plane, along with a handful of...