I think of all these kooky young men who go out and shoot people. Yes, there are things in life worth being depressed over. But there's an inability to distinguish between mourning and depression. Grieving has a natural terminus. It's a self-limiting illness.
Depression can be interminable, it can come and go.
Just imagine the world without depression. You wouldn't have the Emancipation Proclamation. You wouldn't have art. You wouldn't have science. You wouldn't have zippers or light bulbs.