Airport security has a tough job. 99.999999% of passengers pose no threat. A terrorist attack hurts American morale more than it gets boosted from an averted attack. Reminds me of a soccer goalie: a wonderful save gets lets hoopla than a goal scored at the other end, although they have the same net effect on the score-sheet.
Banned from profiling based on the demographics of prior perpetrators, security is limited to treating every passenger with the same routine or with the same chance of an enhanced routine. Is this a good thing? Think of the quantity of available security energy that can be allocated among passengers. Every unit spent on a low risk passenger is effectively taken from the extra time that could have been spent on a high risk passenger. Deciding who is a higher or lower risk is easier said than done though, right?
Each airport has its average demographic mix of passengers. Pretend that Martians have been the demographic group with the most attackers. At the same time, Martian attackers make up only a sliver of all Martians. If Martians are typically 15%-16% of the airport's daily passenger mix, then there is no signal of anything askew. When this % rises, perhaps the airport could spend more time on this demographic since something out of the ordinary is occurring. The idea being that attackers would be additive to the typical mix.
Knowing this, a would-be attacker would have to leave his abettors behind in order to minimize his chance of being detected.Otherwise the demographic spike would alert authorities. Alternatively, he could bring in abettors of different demographics but that seems unlikely due to how affinity groups are often composed. This leaves him more vulnerable to obstacles such as fisticuffs and second doubts. Not foolproof by any stretch, but an improvement in an area where every edge counts.