Are you afraid to die?—"Thoughts of a Dying Atheist", Muse
I've heard a lot of speculation here and there about a link between depression and atheism. It certainly makes sense to Christians that without God and a life purpose, there's just no reason to get out of bed in the morning. And there's enough circumstantial evidence that you don't have to be living under a rock to believe it. But I suspect the majority of Christians only (knowingly) know at most one atheist personally, so I would take any generalizations about atheists from the mouth of a Christian with a grain of salt. Heck, I don't think most atheists are qualified to talk about atheists in general.
But it might surprise you to hear that I do suspect there's a link between depression and atheism, just not the way you might think: I'm not convinced that atheism causes much if any depression, but I do suspect that depression causes a lot of atheism, in a manner of speaking. Specifically, I propose that atheism is more natural and easier to accept from a depressive mindset than from a typical "well-balanced" mindset.
Cause and EffectEmotions have a bigger effect on reasoning than it's comfortable to accept. Marvin Minsky proposes in The Emotion Machine that the division between emotions and reason may even be an artificial notion. I find from my own experience that my mind just works differently when I'm upset, and sometimes the differences are bigger than the similarities.
Someone who sees the world from under a shadow isn't going to see a divine underlying plan in everything that happens, or see little victories as a clear answer to prayer. They don't expect everything to magically work itself out in life or after death, and more often than not prayer won't give much comfort when they're having problems.
But even that's not all there is to it.
The Skeptical MindsetWhen I get a heartwarming email forward, or hear a factoid from a motivational speaker, my first instinct is to check it on Snopes, every time. It doesn't matter if it's a good story, or if it makes a really good point, or if I think the teller is trying to trick me. The bottom line is, if it purports to be a true story, and it isn't, I don't want to be retelling it. And I've been shocked before by what convincing yarns turned out to be false, but I'm getting pretty good at sniffing out fabrications.
I bring it up because most people, under some conditions, just won't bother checking all the facts. It's tedious, and by the time you've confirmed all the facts, all the emotional punch is gone. A lot of those people, for whatever reason, gravitate towards religion, and the fact checkers gravitate away. There are just too many uncheckable facts.
Why it MattersA lot of people would probably read my claim and say, "Oh, another reason to write atheists off. They don't believe in God because they're depressed all the time, but we emotionally balanced people can think clearly." I think that's a bit unfair. I'm not so sure there is an "unclouded reason" in any emotional state, or any "unbiased" default mode of thinking. My skeptical mind helps me investigate bugs in the software I deal with at work, and I think engineers, doctors, stage magicians, and judges need a similar skeptical mind to do their jobs properly. There are problems amenable to a sober mind and problems amenable to a cheerful mind.
If depression is part of the reason behind atheism, though, it does imply that God may not be the one and only cure for said depression. Usually God comes first, then depression, then atheism.
Depression medication won't necessarily "cure" atheism, either. People don't always take psychoactive meds consistently, and seeing their entire mindset change when going on and off the medication can make them question everything they used to believe. A lot of medication won't even dampen the skeptical nature, since that's not the problem it's designed to fix.
But Then Again...I only come into contact with a specific population of atheists, so I'm never convinced that I've seen the whole picture, but I do know a lot of atheists who are on or have been on depression medication, and those are just the ones who talk about it. Still, it's possible it's all in my head, and atheists aren't any more depressed than the rest of the population.