Robert Spencer distills the simple reason for his advocating an unabashed policy of  profiling airline passengers to give greater scrutiny to those (whether Arab, Asian, Caucasian, Hispanic, etc.) who might be Muslim:

Why not? All the September 11 hijackers were Muslims. So were the July 7 London bombers. And the Madrid train bombers of March 2004. And on and on. All the plotters in the recent international airplane hijacking attempt are Muslims. All were working on the basis of Islamic theology. Why must officials continue not to notice this? To ignore this is to give up voluntarily the one thing that may make it possible to spot the perpetrators of a terror attack before it happens, and head it off. In other words, it is suicidal. . . . (article)