It could be argued that all industries sell depression, as selling or even freely offering anything implies that you want it, which would imply that you are currently suffering from a lack of it. The pursuit of anything could be viewed as a symptom of trying to fill an unfillable void in oneself. The only thing, in this view, that DOESN'T constitute selling depression, are things that negate the will directly.
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Same principle as political comics, the value is that people feel the comic removes a mask from reality and depicts how things really are, thus qualifying it as essentially more referent to reality than reality itself. But of course this is only ever just a reflection of their own internally constructed internal reality, and they pick the comic that is the best mirror of that.