In the recent story about the airline passenger with a serious TB strain, the passenger got back into the US despite a border alert to detain him at entry. The border agent who processed him knew of the alert, but let him through because the agent decided he didn't look sick.
In my quest to understand human decision making about security, I've been reading a book on Human Judgment and Social Policy (by Kenneth Hammond). The book discusses two competing theories of truth: in the coherence theory, truth is based on logically consistent conclusions derived from facts; in the correspondence theory, truth is based on accuracy relative to observation (such as our expectations for weather reports). Neither theory is superior in all situations. However, the correspondence theory apparently works fairly well with perceptual observations, but not as well with abstract or conceptual observations.
The border incident seems an excellent example of the last point: the agent relied on his perceptual assessment of the suspect's health, rather than on the conceptual warning that he could be very sick. The agent expected TB to manifest itself visually. Even growing up in a time and place with no serious TB threat, I hear "TB" and imagine people with sunken faces and furious hacking coughs. That image persists despite my recent reading of Mountains Beyond Mountains (Tracy Kidder's engaging book about Paul Farmer's fight against disease in impoverished areas). If the agent had similar associations, he might reasonably conclude that the suspect probably wasn't sick.
Ultimately, this case shows the tension between security and convenience. When I want security, I'd expect border agents to be at least as strict as the warnings (detain additional people as they judge necessary, but adhere to all alerts). When I want convenience, I'd like to see them use their judgment and not hold up people or the processing line when they see no credible threat. In this specific case, with a particular person named, the decision should have favored security. But so many of our security policy statements are phrased much more vaguely (such as the now common airport refrain urging passengers to report suspicious people or bags to authorities). Interpretation must be allowed to navigate these cases which cannot be described precisely. I'd love to see some reporting on this case that discusses this context and tries to get at the relationship between specificity of warnings and how they get applied.