There's a fair bit of academic understanding around depression, mental health and cognitive function in general - the problem is so much of it feels counter-intuitive.
As poster Ablana suggests, there isn't always a big plan behind suicidal acts, nor is it always tied to depression: http://www.health.harvard.edu/blog/suicide-often-not-preceded-by-warnings-201209245331 If you think about this, it makes sense - figuring out the right way to do it requires research and planning. You can't think too much about it without considering consequences, including what happens if your plan fails.
There's nowhere near enough information to conclude what exactly happened with the Germanwings pilot - there may never be - but it does help to get into the headspace of depression a bit to see how it may have led one man to murder many.
Picture yourself in a vibrant world full of smiling, happy people; everyone's enjoying life, having a good time. Then imagine a glass partition lies between you and them. Beyond that invisible wall, the smiling people start smirking or outright laughing at you. Or maybe they simple ignore you're there. Your little glass cubicle starts to fill up with water, obscuring your view of the people beyond. The water gets darker, heavier, and before long the world right beyond your barrier is entirely lost from sight. If the pilot felt like this, if his depression was severe enough, he might not have really had any emotional connection with the consequences of his acts on others.
Depression can also repress all the neurochemicals that make us happy, engaging, or competitive - food loses its taste, jokes lose their humour, sex provides no pleasure. Self-injury becomes a way to feel SOMETHING other than the dull ache of loneliness that envelops the individual like a shroud. Severely depressed people can also feel like an illness, a source of pain for those they love the most. You wouldn't tend to think of suicide as an act of altruism, but for people who feel less than worthless, that's the frame it can take.
Kinsella raises a timely and thought-provoking question about depression and employment. Of course, people with mental illnesses like depression or schizophrenia or conditions like ADHD and autism are already excluded from much of society. An introvert may be the best choice for a job that involves operational skills, but if they aren't one of John Tory's aggressive golfers, will they get noticed? What about an autistic kid like Jacob Barnett - if his parents hadn't taken a significant gamble, he could have been packing groceries at Wal-Mart instead of becoming the next Einstein. That's a key point; we have understanding, medicine, tools and training to mitigate the negative impacts of mental health concerns to the same degree we can manage diabetes or HIV. What we lack is a culture that wants to do this. Mental health is the left-handedness of our time.
Here's where I'll get controversial.
Depression is a seen as a social negative, ie something to be contained or removed. If depression gets tied to acts of murder, there will unquestionably be a crack-down on people with diagnoses of depression, driving admissions even lower. It won't matter, though, because the internet allows potential employers to scour every public facet of a potential employee's life; if you've posted some depressing thoughts on Twitter or Facebook, what impact will that have on your ability to land work? If people crying out for help on the most anonymous platform we have are punished for doing so, what will that do to worsen depression in general?
If you're an employer, you might say "not my problem - I'm looking for the best so I can be the best for my clients/most competitive in my sector." Survival of the fittest, etc., with the spoils going to those best able to take them through persuasion, persistence or force.
So now picture yourself as an Alpha hustler, aiming for fame and fortune, unwilling to let anything or anyone get in your way. It's a bit like the rest of the world lies behind a glass barrier, with those blocking your Critical Path presenting themselves as obstacles, those who can support you serving as stepping stones and everyone else - they just fade away, like Jack slipping between the water in Titanic.
Depression isolates the individual, but so does narcissism and sociopathy, also considered diagnosable mental health conditions. Narcissists and sociopaths are really good at taking from others and have little regard for the impact of their actions on others. Yet these are the sorts of people who rise to the top, elbow their way into the corner office or the Prime Minister's office.
While their actions can certainly be self-destructive, they tend to be pretty good at fending off the consequences of those actions through charm or threats. Sociopaths are pretty good at holding grudges and have no problem using fear and force to achieve their goals.
We've seen enough high power people break the law and social conventions for personal gain; we don't like it, maybe, but we generally accept that that's how the game works.
But what about when sociopaths make choices that impact the lives of others? What if sociopathic politicians do things like cut science research, demonize minority groups or wage wars for tactical political advantage?
Is there a difference between a man with depression crashing a plane and killing all the passengers and a sociopath ordering the direct (a bombing, say) or indirect (cutting of needed services) death of others?
You can draw a lot of inferences here, but please understand my intent is not to pick on individuals, but the cultural context. Mental health is on the radar in a way it wasn't even a couple of years ago; the correlation between work and conditions of work, mental health and productivity are also being seriously discussed (think police, PTSD and the avoidable deaths of mentally ill civilians).
We're talking about mental health, and some of us are actually starting to get how critical an issue it is to everything from driving behaviour to parenting ability to innovation, but by and large we still don't get mental health.
It's a bit like germ theory - we accept that people get sick, but assume getting sick or not getting sick has something to do with personal "toughness" or black magic and nothing to do with hygiene and environment. It's interesting that anti-vaccine people use very similar arguments to anti-med for mental illness folk do, with the importance of environment being down graded in both cases.
Kinsella is right to ask questions and raise concerns about depression and performance (especially around positions that are responsible for the lives of others), but that's just one part of the elephant.
The ability and even desire to kill another human being as though they were not human - that's mental health. The desire to put self-interest above all else, even the well-being of others - that's mental health. The creative impulse, the oxytocin benefits of giving to charity or the urge to push past human limits with cocaine and hookers on Wall Street - that's all mental health.
There are no clear-cut answers to how we should handle all of this, but that's because there isn't any set-in-stone image of what we're supposed to be. As the collateral damage of our resistance to tackle mental health head-on mounts, though, there's a wall we're pushing up against as to how long we can ignore the complex truth.
Like a tidal wave, there's only so long a wall can take constant barraging before it breaks down.
Which is why I remain rationally optimistic about where we go from here.