It works two ways. During the Gulf War, members of the SAS were chosen because they could 'pass' as Iraqi amongst the people of Iraq. Terrorists will find people who can 'pass' and use them instead of someone getting on a plane with a turban or AK-47. Imagine the following scenario. An innocent mom is told that if she doesn't carry a small package onto the plane in her carry-on luggage, her children will be killed. Hey, she's gonna carry the package on the plane. Voila, the C4 or Semtex or whatever is now onboard. The only way to ensure security is thorough searches of EVERYone and EVERYone's luggage, regardless of ethnic origin, appearance, etc.