Percent having had a mental illnessI strongly suspect that this is real, and not just an artifact of the survey, but there are some things to say about it.
Extremely liberal 30.0
Slightly liberal 12.1
Slightly conservative 7.8
Extremely conservative 5.1
First, the results are self-reported, and I am pretty sure that American conservatives have a stronger bias against mental illness than liberals do. In some of the leftist groups I have known you would feel left out if you didn't have a mental illness to talk about. So I think some of this result comes from leftists being more willing to call common sorts of mental troubles "illness" than conservatives are.
I doubt that explains the whole thing, though. I think that statement applies to liberals nearly as much as it does to leftists, and liberals show much less mental illness; I suspect the size of this effect is about the difference between liberals and conservatives, or at any rate no bigger than that.
I think there is a real relationship between far left views and mental illness. The far left people I know are motivated by a sense that life in our society is unsustainable. Our world is too cruel, too unfair, too unsupportive of real human needs, besides which we are trashing the planet and headed for ecological catastrophe.
I think this outlook is strongly correlated with depression and anxiety. The more sensitive you are to human suffering, the sadder you will probably be, and, maybe, the more you long for some kind of radical change to fix things.
That being said, leftists might be functioning as the canary in the coal mine here, at least as regards the psychological trauma of living in our world. If our world were too cruel and unfair for human flourishing, you would expect the effects to show up first in highly sensitive people with a tendency to mental problems.
Plus, crazy people gets votes, too, so in a democracy you can't write off the views of people you think are crazy.
But I also wonder about the relationship between mental illness and politics in other, broader ways. To what extent are political beliefs psychological coping mechanisms? Or, to put it differently, to what extent can political beliefs serve as psychological coping mechanisms?
Consider the ML King/Obama belief that the long arc of history bends toward justice. Might this be a way of remaining hopeful about the future despite current troubles? And wouldn't it motivate you to act, politically, in certain ways? The reverse sort of nostalgic, things-used-to-be better conservatism also seems to me to often function as a psychological mechanism, upholding the possibility of good in a fallen world.
Some people really want to believe that the world is just and not merely randomly good or bad, and I wrote here back in 2015 about the political implications of this attitude:
People who strongly believe in a just world have been shown to be prone to blame sexual assault victims, more willing to malign people suffering from minor illnesses, less compassionate towards victims of spousal abuse. A 1975 study found BJW correlated with a tilt towards authoritarianism, an admiration for political leaders, and contempt for the underprivileged.A case could be made that tribalism of every sort is a mechanism that protects psychological health. After all we did a lot of our evolution in small groups surrounded by hated outsiders, and I think a sense of belonging to a group that is good and opposed by enemies who are bad does a lot for many people. When I confront people who hate whole groups of others, I often feel that I am staring into an abyss of pain, which has been turned outward to protect a wounded self.
What we do, day to day, is struggle to feel good within a particular technological and social world. Politics, I am convinced, is one of the ways we do that.