A hostile nation with nuclear weapons launched a missile. If you're going to take precautions, that's approximately when the cost/value proposition starts making sense.
Sure, I don't actually know the threat level here, and you could well be correct that this was an appropriate calibrated response. My only argument is that the US have strayed very far into "inconvenienced" territory (forgetting we had any compunctions about torturing people, spying on everyone in the developed world, attempting to entrap entire communities of people based on their religious affiliation) by using the "it's for national security" excuse. Americans would be well advised to be skeptical each and every time that excuse gets used.