I am not against training crews in self defense. I'm just not sure how effective it would be against another 9/11 type of scenario.
Shortly after 9/11/01 I took it upon myself to attend a defense course designed specifially for airline employees. The school is called Modern Warrior (see www.modernwarrior.com) and they are a well respected, highly trained martial arts experts. It was certainly a positive experience and raised my self confidence.
However, martial arts is a skill that requires constant practice and dedication. Even annual refresher courses would not be enough to counter people who are well trained and determined to carry out terrorist acts.
Our best defense now is intelligence, vigillance (ie: the AA crew who stopped the "shoe bomber"), non-complacency (religiously following newly established security measures), and strength in numbers. In the post 9/11 world, every passenger has a responsiblity in the defense of the aircraft. Everyone should know that the days of being held hostage for political reasons, and flown to Cuba or elsewhere, are gone. Any hostile act on an airplane, without exception, should be treated by all as an attempt to gain control of a guided missle.
Terrorists are not interested in just harming people on an airplane. That was their method of gaining control of the jet. By sealing and securing the flightdeck, we remove the motivation for them to even be on board in the first place.