You must be discounting MH370 and the 'Alps Incident', that maybe could have been prevented with an even more thorough examination.
Or perhaps 'background checks' may have been the way to go in those circumstances.
For starters this was not suicidal tendencies but pre meditated pre planned and executed murder by a very disturbed psychopathic type personality
7 out of 10 mass murders are by people with no serious mental history!
These type of people are very manipulative and good at covering up so my guess is extra screening will only highlight people who have no mal intentions to others only to themselves!
Also consider any medical is a snapshot in time.no one knows of a trigger event a month after the medical?
All that will be achieved is to drive pilots away from their AME and GP and into the hands of quango or alternative medicines ((
Pace