The thing is that being, for example, Arabic looking or having an Arabic sounding name isn't a prerequisite for being Muslim. So if we started profiling for peo

The thing is that being, for example, Arabic looking or having an Arabic sounding name isn't a prerequisite for being Muslim. So if we started profiling for people that we thought were Muslim, then it would be pretty easy for terrorists to figure out our criteria and just use the most "white-seeming" of their cohort to commit attacks. If, on the other hand, you randomly select people for additional checking, they can't predict that and can't learn how to circumvent it, they just have to take a stab at an attack and hope they don't get unlucky. Basically, any deterministic aspect of security is predictable, which makes it vulnerable.