Because profiling is profoundly counterproductive. The vast majority of passengers are not interested in murder or mayhem, and will report suspicious behavior. If you antagonize one class of people, you reduce their willingness, as a group, to cooperate with authorities.
Also, because terrorists are rare and are not exclusively members of any one profile, you are more likely to miss one if you shift focus onto one group in particular.
"If you antagonize one class of people, you reduce their willingness, as a group, to cooperate with authorities."
The question is whether this effect is stronger or weaker than the gains you get from profiling.
The middle solution: Anti-profiling. It's not about going after certain groups, it's about ignoring certain groups that are harmless.
We don't need to focus on:
-70-year-old British grandmas
-4-year-old children
-Chinese women
-etc.
Obviously this doesn't preclude someone slipping something into their bag without their knowledge, so bags would still have to be checked.
But at the end of the day, there's a lot of simple things you could do to make the whole process faster and easier for everyone, including 23-year-old Arab men with congenital overactive sweat glands.
It's the profiling part that's the problem- you can determine through trial and error if you are likely to be interviewed, and adjust your resources accordingly. As noted in the paper, the 9/11 hijackers appeared to do exactly that.
Completely random interviews can't be gamed the same way.
Not all profiling is based on race/religion. If my country X is currently at war with country Y, it seems like it'd be reasonable to give a second look towards anyone who has traveled to Y and potentially its allies. And vice-versa I would expect Y authorities to profile against X. My understanding is that this type of profiling is currently done in Israel and they claim it to be very effective. I don't know if that's true, but at the very least it seems "civilized."
Russia recently annexed Crimea. Is it reasonable for Ukraine to take a second look at Russians traveling to and from their country? Is Ukraine uncivilized? Is Russia?
Also, because terrorists are rare and are not exclusively members of any one profile, you are more likely to miss one if you shift focus onto one group in particular.
http://www.pnas.org/content/early/2009/02/02/0813202106.abst...