There are appears to be a parallel with pilots who decide not only to kill themselves, but people who commit mass murder and then kill themselves. This is nothing new btw...as far back as the mid 1990's the FAA has been looking seriously at pilot suicide. I am linking here an interesting Washington Post article from a year ago: http://www.washingtonpost.com/...
There is also a phenomenon supposedly with some pilots that have developed mental health issues due to flying, that they never had any history of. Many pilots have to distract themselves with other things instead of staring out the window ahead of them on long flights, as this can be fatiguing and dangerous. It's hard to say, but maybe every flight needs an air marshall that has access to the cockpit. Food for thought.