mood disorders are more common in certain professions, ones where it would be erroneous to call unproductive. Suicidal ideation correates with divergent thinking and creative achievement in a sample of undergrads.

Yes, people with divergent ideas are more likely to be exiled.

There is a new theory that depression in some may be due to mild brain damage, possibly caused by high fat diets, pollution, and lack of exercise. Evidence for this by its high percentage in industrialized society compared to egalitarian [sic] cultures,

There are also many cultural and structural differences between industrial and pre-industrial societies, e.g., as Paul Graham mentioned in this essay:

Teenage kids used to have a more active role in society. In pre-industrial times, they were all apprentices of one sort or another, whether in shops or on farms or even on warships. They weren't left to create their own societies. They were junior members of adult societies.

Teenagers seem to have respected adults more then, because the adults were the visible experts in the skills they were trying to learn. Now most kids have little idea what their parents do in their distant offices, and see no connection (indeed, there is precious little) between schoolwork and the work they'll do as adults.

And if teenagers respected adults more, adults also had more use for teenagers. After a couple years' training, an apprentice could be a real help. Even the newest apprentice could be made to carry messages or sweep the workshop.