The real tragedy in this matter is that the sky-rage events have not yet resulted in training for cabin problems or crew intervention.
Things such as scalding coffee and fire extinguishers are great weapons for defense. Seat cushions are good shields from knives.
In the USA, people are asked to operate emergency exits and doctors are commonly solicited for an ill passenger.
If the certified law enforcement passengers were given a price break or the likely able-bodied-passenger was simply selected to be on standby fo an intervention, the hijackings would be far less attractive.
There are pragmatic solutions available.