The Washington Post offers very sensible words on the lack of common sense in how Homeland Security handled the Cat Stevens incident:
Some of the intelligence reform legislation pending in Congress does call on the DHS to make the procedures surrounding the lists more transparent. But it is doubtful that any system that runs by automatic procedures, as this country's does, will ever be able to deal sensibly with individual cases. Whatever money the former Cat Stevens may or may not have given to terrorist organizations, was it really necessary to stop his plane in Maine? It's unlikely that he is so dangerous that his plane could not land at Dulles, and very likely that the grounding was ordered solely because security bureaucrats were following inflexible rules, without thinking through the consequences. What was missing was common sense.
When I flew to Amsterdam and back in November 2001 -- just after 9/11, I saw how Europeans do passenger screening: with intelligence. The screener looks you in the eye and asks you questions as an experienced police interregator (or defense attorney) would do -- out of order in time sequence, trying to catch you in an inconsistency. Every time I've flown in the US since then, I sense rote following of rules, not an intelligent agent.