Christopher Hitchens eloquently expresses what many of us are thinking. An excerpt:
It's getting to the point where the twin news stories more or less write themselves. No sooner is the fanatical and homicidal Muslim arrested than it turns out that he (it won't be long until it is also she) has been known to the authorities for a long time. But somehow the watch list, the tipoff, the many worried reports from colleagues and relatives, the placing of the name on a "central repository of information" don't prevent the suspect from boarding a plane, changing planes, or bringing whatever he cares to bring onto a plane. This is now a tradition that stretches back to several of the murderers who boarded civilian aircraft on Sept. 11, 2001, having called attention to themselves by either a) being on watch lists already or b) weird behavior at heartland American flight schools. They didn't even bother to change their names.