The tactic of using an airplane as a missile was only valid until 9:57 AM on 9/11/2001. An airplane full of ordinary Americans figured out the security equation over a field in Shanksville, PA. The hardened cockpit doors made double-sure immediately thereafter.
So, the public risk has been eliminated. There are private risks – getting on an airplane with no security screening would be minimally more risky than getting on an airplane with full strips and body cavity searches, but there’s a tremendous privacy and cost benefit to the former. The risk differential is a smaller margin than encountered when deciding what kind of motor vehicle to drive, but these are the kinds of risks a free society leaves with the People to decide.