No - I want to unbuckle to stop anyone moving down the aisle before they get to the door, to the flight attendant, to whatever moron thing this person has in mind.
I think this particular passenger wasn't scared of flying and completely understood what was going on and intended to commit suicide; this wasn't panic - this was premeditated. Passengers did grab him and pull him back into the plane.
But that was this time. If that passenger had something else in mind it's in the best interest of the passengers to react rapidly. If, like 9/11, this was a distraction for a more involved scenario, squelching it is imperative.