First, from a European point of view, the "I'll sue your ass for not telling me the sky is blue" way of handling responsibility has caused any identity (government, business, neighbor, colleague, celebrity) that cannot hide in anonymity to be overly cautious. Any acceptable risk of danger is offset by the enormous danger of due compensation if something does go wrong.
Secondly, the government is, due to their required independence, by definition an onlooker with regard to the communities they have to watch/control. Could we easily tell from carefully watching a box of thousands of bouncing rubber balls which ones are behaving differently from the others when it all looks like a blur? Surely, each individual ball would notice discrepancies upon encountering such an outlier, but this cannot be expected from an outsider.
Thirdly, and this combines the first two, the best the onlooker can do to exclude any false negatives in its selection procedure, is to make sure any voluntary irregular behavior is absent, so that the irregular ones are more easily distinguished. For that same reason any, maybe in itself harmless, strange behavior at airports is dealt with as if it were the real thing to discourage such behavior in the future. The assumption is, of course, that the odd balls are unable to act as normal as the regular ones.