> if a given test were to generate a false positive, you would expect that it wouldn't generate a false positive the next time if run on the same article I don

> if a given test were to generate a false positive, you would expect that it wouldn't generate a false positive the next time if run on the same article I don't think that's true. Remember that the test doesn't actually detect bombs. It detects certain chemicals. Now, sometimes it might just randomly report a false positive and then you'd expect it not to trigger the second time. But some of the chemicals it is built to detect can be found in everyday products, such as hair products, soaps, some medications, and--as I learned today--bug spray. And so for those chemicals, it's going trigger repeatedly because the chemical it's looking for really is there. So that second failure mode is actually pretty common, and so even when that happens, it's normal to take the person into a side room, search them more throughly, talk to them for a few minutes, and send them on their way. What we see here is quite different. Which leads us to the real reason, which you wrote: > It's not that such behavior is automatically suspicious, it's that the behavior is still almost indistinguishable from those who previously have caused terrorist attacks. That's precisely profiling: "the bad guys have profile x and you fit profile x, so we think you are suspicious" where x isn't inherently suspicious. It sounds like you're saying, "profiling isn't such a bad idea", which I strongly disagree with, but I suppose that's a different discussion.