[mburbank]

See, the thing is, one of these days there almost certinly will be a major terrorist attack during an alert. By then we'll be as accustomed to them as car and fire alarms which are omnipresent and utterly useless.

Moreover, to tell people to go ahead with their travel plans while also telling them you have a credible threat that Al Quaeda plans to use airplanes as weapons, credible enough to raise a terror alert, is pretty confusing.

Sooner or later there's bound to be a terrorist event on American soil again. If it happens when the alert is yellow or lower, everyone will want to know how they missed it and the system will seem irrelevant. If it happens when they're on high alert, everyone will want to know how they failed to prevent it when they knew enough to be on high alert, and the system will seem irrelevant.