The underwear bomber was from Nigeria, not the Saudi Arabia or anywhere else. Sulayman al-Faris, also known as John Walker Lindh (a white American), was in training to be a terrorist before he was captured in Afganistan. These are just two of many examples you can find of Islamic terrorists (or would-be terrorists) who are not of Arabic descent. If you branch out from Muslim terrorists, you can name many more. Timothy McVeigh, the Unibomber, the entirety of the IRA, etc.
Use of racial profiling is akin to narrowing your gaze to peer at fewer people, thus allowing atypical looking terrorists to slip through easier than if we impartially screen passengers with respect to race.
And if we adopt a full-on racial profiling regimen, is anyone really convinced that the terrorists won't figure that out pretty fast, then exploit the gigantic hole we've created?
Can America really even keep any policy a secret anymore with the way our media works? If the TSA switches to that, the ACLU will be sending out a press release on their high-profile lawsuit within the very day they discover it to every corner of the earth.
The problem isn't with how racial profiling mistreats minorities -- it does, but it's a worthwhile sacrifice to save lives if it did given a screening at the airport isn't a big deal so long as false positives do not occur -- the problem is that it does the opposite of what it's intended to do. It creates a weakness, it does not shore one up.