And this is why someone a long way away form the investigation, with only media reports of ideas and conclusions, is about to weigh in on the mental status of the copilot of the German Wings aircraft that crashed in the French Alps. I've heard and read that "He was depressed" and "He suffered from clinical depression." And all my hackles come up--the annoyed ones and the scared ones both. Because those statements imply that depression not only leads to suicide (which it does) but mass murder (which it doesn't). And those statements can put in jeopardy the freedom, the educational and employment opportunities, of people who have clinical depression but may now be seen as a danger to others. And that's a very bad thing indeed.
I have known people who killed themselves. Themselves. Not over a hundred other people, strangers. That's an important distinction. Suicide as a result of depression exists, is known, is well-characterized. Had the co-pilot been depressed enough to kill himself--shoot himself, take poison, etc--I would agree--he was depressed.
But not all suicides are caused by depression. Some are caused by a different form of mental illness, and the one that causes people to kill others AND themselves is commonly seen in the murder-suicides committed by angry men (occasionally women, but much more commonly men.) Men who feel entitled to something, who are furious that they aren't getting what they want, or are losing something they think they're entitled to (a wife, a child, a business.) The men who kill girlfriends, wives, ex-girlfriends, ex-wives, and then kill themselves to avoid punishment...they are not depressed, they are angry and defiant. The men who blow up or set fire to their business when they run into debt, or have tax problems, are not just depressed--they are angry, defiant, and want to make a big loud messy statement of how pissed off they are. The men who "go postal," who attack other workers in their place of work, or another place of work, are not simply depressed--they are angry, they feel that they've been lied to, or something taken from them (a job, a raise, whatever) and they're taking vengeance. The boys who shot up Columbine High School, the man who shot up classes at Virginia Tech, the woman who gunned down colleagues at a faculty meeting--they were not depressed, but angry. The man who flew his private plane into the IRS building in Austin, Texas because he didn't believe he should have to pay taxes intended to die--but also to "make a statement," and do damage and kill other people in the process. He wasn't depressed--he was angry, hating, a man with anger issues and control issues who was furious that he was expected to obey a law he didn't like, and that his wife was scared of him and wanted to get away from him.
It's true that depression can co-exist with personality disorders such as narcissistic and antisocial personality--both often associated with anger and feelings of entitlement (Riley et al) (Fava)...but depression in itself is not the motivation for harming others. Anger plus depression (not uncommon in PTSD and traumatic brain injury) is a dangerous combination, but it's the anger component that risks the lives of others. And in this case, the co-pilot's decision to take the entire crew and passengers of the aircraft to die with him reeks of a vindicative, angry desire to get even with something or someone or some organization...to make that big loud statement, to kill innocent strangers when he couldn't get at the people he was really mad at.
Though depression and anger were linked in Freud's conception of depression (that suppressed anger was behind all depressions) and unipolar depressions with overt expressions of anger are now being looked at as a specific subtype of depression (article by Brooks in JAMA Psychiatry), the same article (and others) admit that those depressed persons who express anger and act out some of it also have significant comorbidities--personality disorders and often substance abuse. Since these comorbities and substance abuse by themselves are known to include erratic, sometimes violent behavior and outbursts of anger, it seems to me more reasonable to consider them the source of the anger and any violent acts.
Astonishingly, despite the obviousness of this--that the people who kill groups of others are clearly angry, defiant, vindictive--often from a base of feeling entitled, feeling that they should have everything their way--you still see, as in this case, "depression" given as the motivation. And it's not. At no point in my worst days did I want to harm others. The people I've known who had depression and then killed themselves did not kill anyone else--just themselves. So saying the co-pilot had depression--suggesting strongly to most people who hear it that a person with depression might decide to kill everyone in a school, or a workplace, or a plane, or a train because of depression (rather than out of anger) is both factually wrong--that's not how depression affects people--and unfair to those who have, or have had, or will have, depression.
Moreover, "depression" is a diagnosis often made in error--people who go to a doctor with entirely different conditions may be mislabeled as "depressed" for months or years. (There was a case in a recent New England Journal of Medicine, about a man who had a progressive dementia and despite displaying the symptoms of dementia--which aren't the same as depression--two doctors called it depression.) It's made in error by the very specialists who should know better--psychologists and psychiatrists both have, on occasion, diagnosed depression in someone who actually had a completely different illness.
So, without a scrap of qualification other than having had bouts of clinical depression, knowing other people who had depression, having known people who were suicidal and some actually killed themselves--and some reading--I'm convinced that this co-pilot may have been unhappy, but he wasn't suffering just clinical depression. Ramming an airplane full of passengers and crew into a mountain takes a different motivation.* It's important to figure out what, and why, because it's the only way to refine the screening for aircrew and prevent (most) future intentional air crashes. Depressed people kill themselves. Angry people kill others (and sometimes themselves.) Some people are both depressed and angry--some angry as part of personality disorders, some as a result of substance abuse, some as a result of traumatic brain injury that affects multiple brain functions--and these people--not all depressed people--are more likely to harm others. The combination of depression with another condition that lowers inhibition, increases levels of anger, and affects executive function is far more dangerous to others than depression alone.
* I have my own guess about that motivation, but for that I have even less data than for the actual state of the co-pilot's brain.