Two points:
Why cannot PAX be told at each step along the line, starting with check-in, that "This is your boarding pass. You'll be required to present it as you board the aircraft." There will always be some who won't have it at the ready, but at least the repetition may get through to the majority, especially the non-frequents.
Point two: Concerning aircraft security, I'm surprised that I've never heard from crew who have been on either hijacked aircraft or on aircraft that had a serious threat (such as Richard Reid). I believe - VERY strongly - that if we could ask any of the PAX or crew on any of the 11 September flights, or anyone in the WTC who happened to be looking out the window having their morning coffee and saw AA 11 coming straight at them, about their views on security, they would very likely support strip- and cavity searches for anyone getting within 100 meters of any airplane.