Its not a choice, it's a chemical imbalance caused by faulty neurology. Recent studies are showing that Psilocybin, the active ingredient in 'Magic Mushrooms' can bridge broken pathways in the brain and relieve chronic depression for up to two years after ingestion.
Everyone may get down from time to time and some may be able to shrug it off, but no one chooses to suffer from clinical depression, which is an agonizing, long-term, debilitating and frequently life-threatening condition.
I have no doubt that the condition is largely rooted in genetics. I also think that the very social handicaps we struggle with contribute in large degree to chronic depression. How can you spend your entire life alienated and excluded, incapable of making healthy human connections and not become depressed?
Solitude may be peaceful, but endless loneliness is torture.