We have. Last time I checked, ....(looking out window)...yes, there's an airplane up there right now. Doesn't look like air travel was stopped.
You're not thinking that the little pause we had during the initial panic meant anything, did it? No, that was not much different than the cops checking the inebriation levels of the victims of an accident before letting them resume their drive home.
And, you don't think there would be panic if terrorists shot down a few airliners? You have advocated widespread availability of short range air defense systems. Just how would you protect the airliners from these systems? How would you respond to maybe five or ten 747s being blown from the skies?